Bad electrical noise in 93 grand am

My brother in law has a 93 grand am,the problem is that it has a bad electrical noise. You turn the gains up on the amp half way or more and the sub starts moving even though the headunit volume is on 1. We put new wires and plugs in it,new alternator,moved amp grounds to different locations,used different amps,different radios,different RCA'S,ran wires above carpet away from each other, and disconnected the alternator with the car running and NONE of this helped.The HU is kenwood(test HU=JVC)Amp Orion 225G4(test amp Poweracoustik)Does anyone have any ideas? This one is the first one I am not able to figure out,any help/ideas greatly appreciated.Thanks,John H

I forgot,when the mids were amped you could hear the noise/whine through them with HU volume on 1 and the car in park. I hooked them up directly to the radio and now there is no noise,also we tried running a ground directly from the battery to the sub amp,but the noise got louder and worse. Any Ideas, John H

We tried different amps,happens with the sub amp or mid amp. Tried different pairs of RCA's too. Any other ideas?Thanks for your reply,John H

When you said you moved the amp grounds to different locations, are you grounding all your amps to the same place?  Are the amps mounted into bare metal?  When working with older amps I found it helps to mount them onto a wood base, then mount the base onto the vehicle to isolate the amp casing.  Sometimes when you mount the amp into bare metal, it creates a ground loop that can add interference.  You also might try running shorter ground cables, generally under three foot is what is suggested.

Ok the amps were on carpet,not mounted directly since we were changing out different amps to verify faulty equipment. so no the amps are not mounted to metal,as far as putting the equipment in a different vehicle,we did that as well. We used my truck as a test vehicle since we both use the same sub amp. His amp worked just fine in my truck. Funny thing is,we put everything back in the way we had it before the alt and spark plug wires went bad,and now we have a horrible noise where as before it sounded great with no noise at all. Yes the wires are supression wires. Is there a noise capacitor on this car like the fords,and new chevy's?Thanks for the replies guys,please keep them coming,John H    

Have you tried adding extra ground wires to your battery and HU? I had a noise problem and I added 2 extra 4 guage ground wires[one to the chassis,one to the engine block]and a 14 guage ground from the HU chassis to the dash support.I do this on all my installs now with good results. Hope this helps...

Ok the noise is gone but there is still another problem,with the amp gain under half everything is fine.But when Its half way or more the subs start moving alotand the HU volume is on one. We tried a different amp and it did the same thing too. any ideas? Thanks for the replys in my other post,they're appreciated.Thanks,John H

Ok it doesn't have the motor noise anymore,but the woofer still moves alot when the gain is set 1/2 or higher. Its not the amp cause we tried a different one in the car,and also verified the amps by putting them in my truck and they had no problems at all.Anyone know this one? I appreciate ther help guys, John H