I would guess that it is something to do with your A/C. I doubt it has anything to do with your radio install, it may just be a coincidence that it started at the same time.
The A/C clutch engaging and disengaging "ticks" and it would also effect your engine's power. A compressor clutch that freezes up will begin to squeal as the serpentine belt slips on it.
If it is still squealing, try turning off your A/C during the noise - if the noise stops you may need to look at getting your compressor clutch replaced.
Sunday, October 12th, 2008 AT 3:38 PM