Trouble Shooting Noise
By: Alan Ward

In this paper, we are going to look at some of the common causes of noise in your system, and how to track down and eliminate their sources. Some of the things this page will cover include:

Common Causes

The Environment. Sometimes the environment can play a role in the noise your system is making. Around hospitals, high voltage power lines, and radio stations (not the public listening type either), you pick up alot of interference. Also, extremely HIGH humidity can cause problems. A cold start on foggy morning can lead to some alternator whine thanks to moisture. For the same reason, corrosion builds up on your electrical connections, causing increased resistance. And the most obvious, you are at a show and keeping your battery topped off with a charger! AC power lines are very dirty, and you should disconnect all sources of external power during judging anyhow.

A poor battery. Check the voltage on your battery with the engine off. IME a good battery will be somewhere around 12.7 volts, plus or minus 0.2 volts.  If you're right at 12, or even under, then try charging your battery.   Constant low voltage is a sure indication you need a new battery, OR have a charging system problem.  Check this link if you suspect your charging system.  If you have a dual battery setup, then it is likely you have more complicated problems.  Differing voltage in a system can be cause for minute annoying little buzzes. Proper power systems should keep a constant voltage (although this is next to impossible, it's what you want to work towards. If you have one battery that's keeping a different voltage, the unbalance between equipment using that voltage can cause interface problems with equipment not using that source.

Bad grounds. A bad ground is probably the most common cause of noise. If one of your audio componants is poorly grounded, it's not getting as much voltage as other componants are. For more on proper grounding, check the appropriate  tech paper.

Isolator whine.  Before proceeding to the next culprit, it is VITAL that you bypass your isolator and make sure it is not the problem.  This is simple to do, and is just as mandatory as checking a fuse when nothing works at all.   To bypass the isolator, unhook all of the wires from it, there should be four wires.  hook the 3 wires from the alternator, battery 1 and battery 2 together (easiest way to do this is with a bolt and nut) BE SURE and tape the assembly off so that an accidental grounding does not occur.  You could also test the system with the alternator unplugged, (engine off of course)

Only after you have eliminated the above possibilities should you begin to tear apart your system and start checking components (unless of course you just changed amps or something and have good reason to believe it is the system).  In the end use your head, think about it logically.  MOST important of all, write down EVERYTHING you find out no matter how insignificant it may sound, if in the end you cannot isolate the problem, and have to drop it off at the store your notes may reveal to a skilled installer exactly what the problem is saving you A LOT of $$.  As you're reading through this, the idea is to eliminate as much of the electronics as you can between you signal source, and your speakers. Then, read each componant till you're done.


  1. You may find throughout this procedure your noise may change in pitch and volume.  This is due to various levels of processing.  To counter act this Set all of your processors, eq curves, bass levels, treble etc to the middle or zero setting, depending on equipment... working upline to a component that amplifies or alters a bad signal, may cause a false assumption. (its amplified or altered now and is misinterpreted as the source, while it is merely amplifying or distorting the source noise.), .........even though in theory it cant amplify a bad component that isn't hooked up (further upline), still good to keep this in mind
  2. Gather supplies:   If you don't already have one go to radio shack and find a cord that turns the headphone output on your walkman or home stereo into an RCA cable.   Use this cable for all source signals during the testing. Also buy about 4 female-female RCA y splitters...(to be used in steps 5 and 7), also have handy an extra RCA cable, at least 10 feet long, or long enough to bridge any two components.
  3. Now your ready for the fun part, what's behind door #1? Unhook the RCA's from each of your amps or the suspect amp, feed it the clean signal from the home stereo... do you have noise?
  4. Check the RCA's:   Again feed a clean signal from the end of the RCA's to each amp. This may require a female-female connector from radio shack, our king-of-connects.  Y-splitters work very well and serve a dual purpose for later on when you test out the crossovers.  Do you have noise?
  5. This step will be repeated for each set of signal processors, in-between each step refer back to step 4, and check each set of RCA's.  AS you move up the line, hook your signal processor up to the RCA's leading down to the amps, remember we already know that every thing in this particular setup is good, so if there is noise, then the processor is causing it.   Do you have noise?
  6. At this point refer back to step 4, and then 5, and then 4, and then 5, etc until your at the head unit.  Each time testing the system with an external source. TAKE NOTES ! ! If you make it up to the head unit with no noise, after having completed step 4 once again... remove the head unit, your problem may be:
  7. Once you have found your faulty component, by-pass it and make sure the system works well without it, this is where the RCA Y-splitters come in handy, mainly if a crossover is your problem.

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