Killing off the sounds you don’t want to hear coming from your custom rig’s stereo system

By Grizz Archer

Hums, whines, buzzes, crackles, pops and other unexpected noises blasting out your rig’s speakers not only ruins tunes, they are really frustrating when you can’t figure out how they happen in the first place.

Anyone who has a good audio system wants clean, vibrant sound. Unexplained background noises ruin the day. So, let’s go noise hunting and kill off the little culprits responsible for the unwanted intrusions!

There are multiple possibilities as to where such noises originate – and they all relate to electrical issues: alternator whine; isolator-induced noise; external-radiated noise; and of course, ground-induced noise are good areas to begin the noise hunt.

To make the job even easier, we’ve listed three specific items to check-off and what to look for in tracking down nuisance noise. (NOTE: It’s wise to write down everything you checked, changed, and the end results. Forgetting and having to start the noise hunt all over sucks.):

Bad grounds: What a nightmare this can be!  Always check the ground wires/cables first if you have a noise problem.  There is a very good chance your noise issues can be traced to at least one of the grounds.  Ground should always be to a bare metal (stripped of paint and primer, oil and soil).  It’s best to use a nut/bolt to attached ground to the grounding surface because bolting down ensures the best surface contact. NEVER use a self-tapping screw; self-tapping screws contact with a surface is usually just the thin threads. NEVER use a seat or seatbelt bolt for the same reason. Using self-tapping screws and bolts holding other items in place are the two biigest – and most common – mistakes when installing a sound system. And such ground mistakes weaken the entire system, causing a multitude of problems including ground-induced noise.

Weak batteries: A sound system needs a strong, steady, even flow of voltage to operate at the optimum performance level. Healthy batteries are critical to a sound system. Low batteries and fluctuations in voltage create noise issues. Check the voltage on your rig’s batteries with the engine off, and check each battery’s cells to make sure all is well. A healthy 12V battery will meter 12.5 volts, plus or minus 0.2 volts.  A cell of a good battery should be between 2.1-2.5 volts. If the battery meters less than 12.3V, it needs charging or replacement.   Consistently low voltage is a result of a poor battery or poor charging system.  When the truck is running, you should meter between 14-15V to the sound system’s power supply. If you have one battery keeping a different voltage than another one, the net voltage will be different than you’d expect.

Isolator whine: If you do not have a battery isolator, then you can bypass this section.  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.  Make sure that the positive wires going to the battery(s) is connected directly to the wire coming off of the alternator(s).  If the noise goes away, then your isolator is your weak link.  If not, then bolt it back together and get ready to go through the next stages.

Other noise-inducing culprits: Only after you have eliminated the above possibilities should you begin to tear apart your system and start checking individual components.

But a cautionary word before going any further: What follows is a mixture of both easy and advanced audio diagnostics. So before you do anything, grab your favorite beverage and ready over everything to see what you might need in order to hunt efficiently.

Now, disconnect the RCA’s from each of your amps or the suspect amp.  If possible, feed the amp the clean signal from the home stereo. Is the background noise still present?

o        NO, the noise ceased: You’re in good shape.  This means the amp(s) and the speakers are OK.  Hook the RCA’s back up to each amp.

o        YES, there is still noise: Bummer. You can assume for now the problem is in the amp(s), speakers, or speaker wire routing.  (It can’t be the head unit or any previous processing since they are now out of the loop. It can’t be a power supply problem because you already checked out the batteries and didn’t find anything wrong.)

The hunt now continues on to three other suspect areas of noise generation:

1)      Speaker mounting/wire routing: Unhook the speakers from the amp and test them from an external source such as running a long wire from a home stereo to the speakers. Is the noise still present?

• YES: Now you know the speakers and the wiring from the amp to the speakers is fine.
• NO: Bummer. Either the speakers or the crossovers (if you have components) are bad. You can test each driver individually in this case in order to rule out the speakers, leaving the crossover as the culprit.

2)      Ruling out amp: If none of the above criteria solve your problem then your amp(s) is probably bad, or the power supply to it.  You can test the power supply (battery and alternator) with another amp you know is good.  If the noise doesn’t go away, then the power supply is the problem.  If it does go away, then the problem is in your amplifier.

3)      Checking the RCA’s: Again feed a clean signal from the end of the RCA’s to each amp.  Use a home stereo and a new set of RCA’s straight to the amplifier.  Nosie still there?

• NO: Good, then your RCA’s are not damaged, shorted, or poorly routed.
• YES: Check the routing of your RCA’s. Also, check to make sure that none of your RCA cables are physically damaged. Damage on the outside may be a sure indication that the inside of the cable is also damaged. Have a spare RCA, a cheap one will do fine. Now, use this cable you originally ran in the car and lengthen it from where the radio is to the home stereo. If there’s no noise, then the RCAs, amps and speakers are all OK, and the problem is in front of these components.

This step will be repeated for each signal processor/component in the audio chain.  In-between each step refer back checking 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 everything in this particular setup is good, so if there is noise, then the processor is causing it.   Do you still have noise?

o       NO: If you don’t have any noise then your first processor or crossover is in good shape, proceed to check the RCA’s leading up to the next level.

o       YES: If you have noise then your crossover/processor, is the problem, likely causes for this may be a poor ground on the processor. Make sure each processor has its own ground and it is not tapped into an amplifier ground.

At this point lather, rinse and repeat: Do what you just did through the rest of the processors until  your tests take you to the head unit itself.  If you make it up to the head unit with no noise, then your noise is obviously coming from the head unit.  Remove the head unit. The problem may be:

1)      Bad Ground: Check the ground on your head unit.  Sometimes the factory ground wire is not optimum.  In this case, find a good grounding point under the dash on sheet metal rather than a ground wire and bolt – don’t screw – the ground wire to the grounding surface.

2)      Poor mounting location: Is your head-unit in an other-than-stock location? Your source of outside noise could be coming from nearby wiring or other electrical components not related to the sound system.

Once you have found your faulty component, bypass it and make sure the system works well without it.  If you have tested everything and all components are good, but there is still noise, well, run for your life ’cause the Boogeyman is haunting your ride!– CR

Grizz Archer is an expert in high-end audio systems and spends the majority of his waking hours marketing and designing components for Soundstream and helping audiophiles  fine-tune and troubleshoot their sound systems.