(888) 737-1752
XBOX360 & PS3 REPAIR EXPERT SERVICE
We can...
It is difficult to diagnos without seeing the vehicle. Does it have a Bose or other upgraded factory system? Not likely in the Quest, but often vehicles have an amplifier that could be bad or lost power. I know this does not answer your question but may point you in the right direction. Try using the Fader and Balance.... Isolate one speaker at a time and see if any sound louder than the others.