Here's another weird one. My "deluxe" factory radio with GPS won't stay turned off. When I turn off the ignition, the radio turns off after a few seconds (like normal), but then it comes back on and stays on until the battery is drained. No combination of turning off the radio or CD manually before or after shutdown will make it stay off.

Is this most likely a problem with the radio or with the electrical system? I don't trust my mechanic to go poking around with at least SOME idea first.

Thanks in advance for ideas!