I have had an alpine CD/Mp3 player fitted to my Audi , when I switch on my cars ignition hence apply power to the system I get a High pitch tone in the rear speakers only .
When the guy fitting tried to use RCA connectors instead this caused an unacceptable popping noise in the speakers so he went back to the ISO connectors.
The noise is there when the car engine isn't running and it tends to come and go.
Anyone got any advice on how to trouble shoot this and can I easily replace the amp or is it inside of one of those side mounted subs ?

The rear amp is a complete waste of time and is only 2x20w