alternator whine thru rear speakers

[89 White LX]

i checked the ohms on the capacitors that bolt on the coilpacks. those are suppose to suppress the engine noise. they tested good. I am wondering if this could be the amp. I have 2 factory amps in the back. when I unplug the amp to the rear speakers the whining noise goes away.
1997 vert with mach 460 system.

any advice?

 

[mixedbreed02gt]

purchase a ground loop isolator.

install it between the head unit and amplifier on your rca wire.

should solve your problem...if it doesn't, you need to make sure your amp ground is touching bare metal (not painted metal)...if not take some 80 grit sand paper, and sand your ground mount area till you see shiny metal, then re-attach firmly.

 

[BlownFiveLiter]

Check the ground in the driver's side kickpanel. They can get a little loose sometimes from bumping/kicking the kickpanel, and then you'll start picking up interference when the system finds an alternate path for a ground.

Edit: Just realized this thread was from June. Issue is probably resolved by now, just had a recent reply which caused me to notice it.