Troubleshooting Noise

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Use a methodical approach to determine which pieces of equipment are causing the problem.  (If you are using a lot of stomp boxes, chances are good that you may have more than one significant noise source to deal with.)  After isolating the problem to a particular component, refer to the table below, paying special attention to the causes and solutions applicable to the problem component.

1. If the problem is obviously the guitar, such as noise that changes a great deal when you touch the strings or jack plate, or scratchy noises when you move the guitar controls, then proceed immediately to the table below to characterize the noise and look up solutions applicable to the noise and guitar.
2. Set up your gear the way you normally play it, using the same gain levels, effects, cords, and guitar as have been giving you problems.  I.e., make sure that the noise you are attempting to cure is present when you begin to troubleshoot.  One exception, if you are using a noise gate turn it off!  Don't forget that a noise gate may be "hidden" in the patch you are using in a multi-effects processor or preamp.
3. Without changing any controls, unplug the guitar cord from the guitar
• If the noise level dropped significantly the problem is the guitar.  Proceed immediately to the table below to characterize the noise and look up solutions applicable to guitars.
• If the noise level stayed about the same or even went up slightly, the problem is almost certainly not the guitar.  Proceed to the next step.
4. Unplug the other end of the cord from the amp (or the stomp box it is plugged into).
   • If the noise level dropped significantly the problem is the cord.  Replace the cord. Note, it's not unusual for an unterminated cord to pick up some noise, but if the cord is well shielded it shouldn't pick up much.  If you want to be certain whether the noise is coming from a poor cord or just because the cord is unterminated, you can place a 10k resistor across the free end (without holding it in place with your fingers, which will introduce noise).  If you do a lot of this sort of thing I recommend a 1/4" inline jack with a 10k resistor across the terminals.
   • If the noise level didn't drop significantly, the cord is okay, proceed to the next step.
5. Work your way all the way back to the amp, repeating the two steps above (i.e. remove first one end and then the other of the connecting cables) for each piece of gear.  When you encounter a drop in noise level you've found a problem component, troubleshoot that component using the table below, then proceed with the rest of the gear.
6. If you have effects in an effects loop remove them one at a time.  When you encounter a sudden drop in noise level you've identified a problem as the effect or one of the cables connecting it.  Troubleshoot using the table below.
7. If you get all the way back to the bare amp, i.e. there is nothing plugged into the amp and nothing in the effects loop of the amp, and you still have significant noise, then use the table below to characterize the noise and look at causes and solutions related to amps.

It is important to characterize the noise because often that gives us clues about the source of noise and how it is getting into our gear.

Noise Type	Description and Common Sources	Causes	Solutions
"Smooth hum"	This is the classic hum often heard when using single coil guitars and also in many vintage tube amps.  The source of this noise in guitars is the 60hz (or 50hz, depending on where you live) electromagnetic interference from building wiring, overhead power lines, and so on. The source of this noise in old tube amps is most often the power line itself.	Unshielded single coil guitar.	Shield and properly ground the guitar's circuitry.  Note that very few factory guitars are adequately shielded or properly grounded.  Even most of the expensive ones are "rank" in this regard.  If the noise actually gets louder when you touch the strings then it is likely that the strings are not well grounded or that the hot and ground wires to the jack are reversed.
		guitar cord	Ensure that the guitar chord is of decent quality, undamaged, and no longer than absolutely necessarily; and that it is not routed beside power cords, transformers, and other noise sources.
		Inadequately filtered power supply (usually in an older piece of line-powered gear such as an amp, powered mixer, preamp, and so on).	It is not unusual for capacitors to dry out and fail in older gear, whether that gear is tube or solid state makes little difference.  Sometimes the capacitors can be "reformed" but more often they have to be replaced.  Have the equipment serviced by a qualified technician.
		Defective, misadjusted, or absent hum balance circuit in tube amp.	Most tube amps have a hum balance circuit in the filament heater supply to suppress noise from the heater filaments.  On some amps this is a potentiometer and when that is the case turning the pot should make some difference in the noise.  If not, the pot is probably bad.  If there is no hum balance pot, the amp still should have fixed resistors serving the same purpose.  If you suspect the hum balance circuit, take the amp to a qualified "tube guru" for repair.
		Large ground loop between pieces of gear.  This happens most often when you are using two or more line-powered (i.e. plugged directly into the wall, not using a "wall-wart" transformer) devices or when your equipment is rack mounted.	Disconnect and insulate the shield braid at one end of the instrument cord that connects the two pieces of equipment.  If you are using a rack, and the problem persists, use insulation washers to isolate the gear chassis from the rack mounting rails.  Never use ground lift plugs! If disconnecting the shield braid killed your output, put it back and look for a ground loop elsewhere (possibly in the rack mounting, if you're using a rack).
"Harsh Buzz"	This is a harsher raspier sound than the hum described above.  While many of the causes and solutions are the same, I've listed this separately because there are some differences.  One such difference is that this noise can often "ride" the power line into gear that is functioning as designed.  I.e. a lot of gear is designed with the anticipation that clean 60hz (or 50hz) sine-wave power will be supplied and the gear doesn't do well at filtering sharp transients on the power line. The raspiness of this noise comes from the sharp edges of the waveform and it is the high-frequency component inherent in those sharp edges that makes this noise much more difficult to shield against (and much more annoying).  A humbucking guitar that is completely immune to "smooth hum" may be obnoxiously noisy in the presence of "buzzing" noise sources if it has an unshielded control cavity or pickup leads or internal groundloops between controls. Common sources of this noise include flourescent lights, computer monitors and TVs, computers, light dimmers, motor controllers in some energy efficient appliances, light sequencers, and even MIDI gear.  Sometimes you can eliminate or greatly reduce this type of noise merely by relocating or reorienting your gear or changing where you stand or the direction you face when you play.	Unshielded or poorly wired guitar of any type.	Shield and properly ground the guitar's circuitry.  Note that very few factory guitars are adequately shielded or properly grounded.  Even most of the expensive ones are "rank" in this regard.  If the noise actually gets louder when you touch the strings then it is likely that the strings are not well grounded or that the hot and ground wires to the jack are reversed.
		guitar cord	Ensure that the guitar chord is of decent quality, undamaged, and no longer than absolutely necessarily; and that it is not routed beside power cords, transformers, and other noise sources.
		Inadequately filtered power supply.	A lot of gear was never designed to deal with "dirty" power.  If the gear has little or no hum, but is susceptible to buzz, and if other possible causes have been eliminated then it may be worthwhile to purchase a good power conditioner to clean up the power for your rig.
		Large ground loop between pieces of gear.  This happens most often when you are using two or more line-powered (i.e. plugged directly into the wall, not using a "wall-wart" transformer) devices or when your equipment is rack mounted.	Disconnect and insulate the shield braid at one end of the instrument cord that connects the two pieces of equipment.  If you are using a rack, and the problem persists, use insulation washers to isolate the gear chassis from the rack mounting rails.  Never use ground lift plugs! If disconnecting the shield braid killed your output, put it back and look for a ground loop elsewhere (possibly in the rack mounting, if you're using a rack).
"Hiss"	This sound almost always comes from within a piece of gear.  It is usually caused by poor circuit design, internal ground loops, poor quality or electrolytic capacitors in low-level audio circuits, and so on.  There is little that the non-professional can do to eliminate hiss other than to determine which piece of gear is causing it and stop using that gear.  In fact, in many cases there is nothing a professional can do to eliminate hiss.  Some stomp boxes and multi-effects units generate unacceptable (in my opinion) amounts of hiss, as do some onboard preamps and "tone boost" modules for guitars.  Sometimes you can reduce the hiss by moving effects around in your chain, putting the noisy boxes after any high-gain effects.	Poorly designed or built item.	Identify the offending piece of gear.  Stop using it or move it to a later point in the chain, after any high-gain devices.
"Crackling"	A scratchy or cracking noise.	Crackling when adjusting controls on guitar.	Dirty or worn pots.  Use contact cleaner to clean offending switches or pots or (better) replace them with new parts.
		Crackling when adjusting controls on amp or other gear.	Dirty or worn pots.  Have gear serviced by qualified technician.
		Crackling only when playing.	Static build-up on pickguard.  Stop polishing pickguard.  Wear short sleaves or wear a shirt of a different material.  Cover the entire back of the pickguard with foil and ground the foil.
		Crackling when the guitar is not being handled or when there is not even a guitar plugged into the amp.	Possibly a serious problem with the amp (especially in the case of a tube amp).  Have the amp serviced immediately or more serious, and expensive, damage may result.
"Popping"	A popping noise.	"Normal" noise when connecting or disconnecting gear.	This is normal.  Switch amp to standby or turn the gain down when connecting and disconnecting gear.  If you need to change guitars in the middle of a set, use a cord equipped with a shorting "quiet plug." Peavey Silent Instrument Cable Planet Waves Circuit Breaker Instrument Cable
		An extremely loud "gunshot" like noise when connecting two pieces of powered equipment.	This is not normal.  You may have a dangerous problem.  Use your outlet tester to check the outlets that both pieces of gear are plugged into.
		Soft popping when switching pickups (happens most often when there is a preamp in the guitar).	This is usually caused by a voltage building up either in a pickup or in a capacitor somewhere in the circuit.  When the component is switched in circuit the charge causes a pop.  Sometimes placing resistors from each switched terminal to ground can help.  Another technique that sometimes helps is to place very large resistors (470k or so) between the switched terminals.  Keep in mind that either technique will probably alter your tone, though.
		Soft popping when touching strings or other metal parts on the guitar.	Your body is probably discharging a capacitor.  If you are using an isolation capacitor between the signal ground and your bridge ground you may need to place a 220k resistor across it (this usually isn't necessary though).  Also, ensure that you didn't accidentally get the capacitor between the jack and signal ground.
"Surging Surf"	A cyclical "surf" sound - sort of like waves rolling onto a beach.	Happens even when a guitar is not plugged into the amp.	Usually only seen on tube amps.  This noise heralds a serious problem that is likely to get worse very quickly.  Usually it means tubes and or associated resistors are failing.  Stop using the amp immediately and have it serviced by a qualified technician.  If you continue using the amp more serious, and expensive, damage is the likely result.
"Ringing" and/or "Squeal"	A ringing sound accompanying picked notes, or going into feedback squeal too easily, can both be caused either by the guitar or amp.  Try the amp with a couple of different guitars to determine where the problem is.	Guitar.	This can be caused by microphonic pickups, poorly mounted pickups, or hollow body guitars with too much resonance.  Make sure that pickup mounting springs (or surgical tubing) are in good shape.  Pot or replace microphonic pickups.  For hollow-body guitars, stuffing a rag or small towel in the body may help, or you might try a feedback suppressor.
		Amplifier.	Almost certainly caused by a microphonic tube.  Usually a preamp tube but it can happen with output tubes, too.  This is fairly common with combo amps that have the tubes hanging behind the speaker.  It's less common on heads and when it does happen there you can sometimes move the head from the top of the cab to a location a few feet away and get through a few gigs, but usually once a tube goes microphonic it won't be too long until it fails completely.  Ironically, I've had NOS preamp tubes that sounded their best just before they went microphonic.