I have a '97 that I just bought a couple weeks ago. I am getting a rather annoying hum in the speakers that changes pitch at times (when cd changer switches songs, turn signals blink, etc). Any idea where I should start looking to track down the source?

 

Sounds like you have an aftermarket stereo that was not installed properly. Read my post on upgrading the C5 Bose system.

 

The car may have had an aftermarket stereo at one point, though I doubt it knowing the previous owner. It's all stock right now.

 

The C5 has a number of modules in it's Bose stereo system rear my post. Any one of them could cause noise to be injected into the audio distribution system. Short of using the "shotgun" method of replacing modules, you need to look at the audio signals with an oscilloscope to diagnose the problem.

Unfortunately it could just as easily be a wiring problem like a bad ground connection somewhere in the harness. Swapping modules will not find this problem, only prove it is not a module.

 

P.S.

It could also be a problem with the charging system. A bad alternator can cause a lot of AC noise that changes with RPM to be injected onto the 12 volt lines.

 

It could also be that the anntenna ground is broken or disconnected. What usually causes hum as 99HT said is ground problems. A stock system could produce these also if the grounds are going but not completely gone. There are several grounds-motor, each bose amp, fuse block, steering column, antenna,etc. Any one of these grounds being messed up can introduce noise to the system. First I would try disconnecting each amped speaker one at a time and test for noise. If you hit the right one, the noise will disappear when it is disconnected. If this happens, lucky day. Check the ground. If its good, take a second amp, plug it in where the first one was and check to see if the noise returns. If it does, its the wires to the amp or the head unit. If it doesn't, its the amp so get a new one.

If you don't loose the noise with the amp wiring, its something else you'll have to track down. All these procedures apply to engine whine. It will sound like a high pitched whine that increases and decreases in frequency based on the engine rpm. If the noise doesn't mimic the engine, its something else, probably a head unit problem.
Lastly, have any of the ignition parts been replaced like wires,etc. Many aftermarket replacement parts lack the proper shielding necessary to keep noise out.
Good luck with the noise gremlin
92TripleBlack

 

I've been told a car stereo hum can also be caused by a bare spark plug wire shorting out on the engine block. The theory is since the ground is attached to the chassis (in most cases), a good amount of current coming from a bare plug wire could travel along the conductive pathway of the chassis until it makes contact with the ground thus causing a hum. It's far fetched, but worth a try. Good luck!

 

Also if you have a aftermarket system make sure that the
amp power wire and rca patch cords arent running next to each other.
This can causing that humming you hear.
;)