High pitch whistle coming from speekers.
 

I have a 69 gto that has a real nice stereo system in it that sounds great when the car is not running. But when the car is running i have a terrible whistleing nose that comes from the speakers. I have tried everything i know to get rid of it, such as groundin each amp seperatly and all together. Two amps one for subs and one for door and deck speaker. I have even totally removed the alternator.
The only other thing i can think of is the msd 6 al box is causing it.
If I switch to a digital box mayby that would do it. Any other ideas would be great thanks!!:)

Check your spark plug wires. You may need noise suppression wires

You probably need a condensor on your coil and alternator.

More than likely it's the alternator interfering with the amps.

You could take the belt off the alternator and start it up and see what happens.

I had similar issue. Careful grounding, noise suppression, shielding, etc...
I have multiple remote amps (7 speaker speaker system). Nothing seemed
to help. Same noise when using GM HEI or MSD 6A.
Finally ended up changing the head unit and the noise went away.

MAke sure your head unit is grounded well; that it has a good electrical connection back to the batt negative. Same for the amps.....just grounding them to local metal may not be good enuf.

If it is the MSD box causing the whine, make sure that none of it's battery connections are shared with any other circuits; i.e. all things should be independently connected back to the battery negative. The batt acts as a very large capacitor, so connecting the radio and amp supplies directly to it will get the benefit of it's filtering.

George

I used to have these problems, and ended up adding a cap and coil to the radio feed wire. I think you can buy the "kit" now from radio shack or an electronics outlet. Break the radio hot wire and put the coil (choke) in line with it. Then the cap goes from ground to the radio side of the choke. That should fix the "whine" issue.
Stu

All hail the LC Low-Pass Filter!!

un hooked the alternator all together and the noise was still just as bad. Still in the process of checking some of the wiring. Thanks for the ideas.

One thing you can try is to disconnect the audio signal cables from your head unit.
Then listen to see if the noise is coming from the external amps. This is what finally
pushed me to getting a DIN style head unit as the shaft units I tried all had noise
issues. I have an inexpensive Kenwood KDC-138 In-Dash CD Receiver ($50-$80)
that solved my noise issue.

Put a ground wire direcly from the chassis of the stereo to the chassis of the car or metal under the dash. Like George suggests you might have to run it all the way to the battery. Use one of the screws on the radio along with a lock washer. On the car chassis side use a sheet metal screw and a lock washer. Scrape off any paint so that you are on bare metal! A 14-16 guage wire will do fine.