Annoying KDC 9520 beep

Just bought a car with a Jensen KDC 9520 stereo in it. I love the thing, except for one detail. There is a LOUD beep every time I push a button. Volume control does nothing to lessen the effects, and neither the operator's manual or tech support line was helpful. Does anyone have this radio or have a clue of how to get rid of the beep? Any help would be appreciated.