19MustangGT90

when i turn on the radio up 2 notches or clicks the volume is normal but then it goes up to insanely loud to really quiet and back and forth , this is the stock radio AM/FM casset that came with the car, what is the problem?is it fixable, or just get a new one? if i have to get a new one does any1 know the demensions it has to be for it to fit in place of thestock one?
-thanks

Chopper

I'd just get a new system.You can start bylooking up Crutchfieldand using the car search feature.