crossfire cfa-602, car audio amp problem

hi

i dont post much but i thought you guys might be able to help me

i have a crossfire cfa602 amp that is making a weird high piched noise about 10 sec after its turned off!
thats with the rca's dissconected, mostly in the right channel and a little in the left.

i know this amp is getting on a bit(10-12years old!) but its 1 of 6 i am using at the moment, this one powers a set of usd HLCD's
if i recall correctly the amp at one stage of its life accidently had its 2 channels wired together, it shorted and blew the 30a fuse in one channel.

was that the likely cause?

anyone with any idears on what it is, i dont have a huge knowege of how they work but i can usually fix most things.

thanks