Ok i have made a few posts now, but i have narrowed down my problem. Everytime the amp turns on the whole speaker system lets out a loud screach noise. If you have not read the other posts i have a 2000 gt with the mach 460 and i also replaced the head unit. Please someone let me know what is up with my amps.

 

I'm no pro, but it might be that the amp needs to be better grounded. Try running a ground from one of the mounting screws/bolts to a decent ground point on your chassis. IMO