a different kind of engine noise

Ok,so I know there's a million different posts about engine noise issues on here already,my issue is a little different though.I already know the basics of tracking down engine noise(ground loops,RCAs ran around power wires,ect.),but I can't seem to figure out this one.I have a 95 Grand Am(3.1 engine,auto).For the stereo I have:A Pioneer DEH-P5900ib deck(bought brand new last year,no problems known with it),oldschool RF Punch 400x4 dsm(running interiors),clean battery and amp grounds,tsunami rcas,4 gauge from bat. to distribution block,8 gauge from block to amp.I am getting alt. whine through my speakers,hissing at low volumes,popping noise when switching from source-source on the head unit(cd to ipod,tuner to cd,ect.),and what has to be the strangest thing of all is when I open my door,then close it,if the stereo is on even at low volume,as my dome light dims down(factory dimmer),there's a high pitched whine-down noise as it dims(like waaaaaeeeeeerrrrroo).I have had issues with this amp since I bought it from a guy along with a Punch 150,and orion hcca 225(dig reference) that said they were all broke.She had a melted power block,but worked on the bench,so I transplanted a block from an old 100ix dsm I had laying around.I noticed when I disconnected my ground from my radio,with the amp and rcas still connected,the radio stayed on grounded through the amps rcas.I have never noticed this before in any other setup.I checked the rcas cords and they are good.I opened the amp to test it and all tested well except I noticed that there was a ball of solder that was near the rca jacks and went from the rca circuit to a random trace on the board.I cleaned that up and hooked it up and checked the rcas and they don't ground out like before,but the noise is still there.It sounds fine on the bench with a battery and trickle charger except for the hiss is still there.When in the car,it's horrible!I can't enjoy the music at low volumes,but it drowns out when you jack the volume up.Any suggestions would be appreciated.Thanks in advance.