Loud noise coming from rear speakers on Mach460

Hey guys i have a 95gt with the am/fm/cass mach460. i just bought the car last fall, i noticed the other day the amp on the right (pass side) was unplugged, i plugged it in and the rear speakers (mid-bass) kicked in. . . sounded good. then a couple hours later i fired the car up and i had a bad "humming" noise (ground noise) coming from the back speakers, with the car still running i unplug the amp and plug it right back in and it sounds good again for a little while, maybe a day maybe only an hour. . . anyone have this problem? If i cant figure out what it is i think im just going to hook a swith up to the power wire for that amp and when it f's up ill just switch it off an on again. . .

Also im about to hook up a new pioneer h/u. . . usually for my other cars i just cut off the factory harness, get a diagram and hook up my deck, but the mach system seems like its a little bit more of a pain in the a-- so shoud i just buy that schosce harness and a 5v regulator?

thanks guy

well, i went and bought the metra kit for it today and hooked up my h/u, its good that my h/u had 3 sets of rca pre-outs because you need one set for the front spk amp and one for the rear spk amp.
since hooking up my h/u i havent had that noise from the rear mid-bass. . .

so if your hooking up an aftermarket h/u to your mach 460 and you only have one set of pre-outs i would recommend getting the schoshe harness becuase you dont need any preouts for that. for the metra you need 2 sets.

well, the noise is back