I have a Vauxhall Meriva Breeze and the radio keeps turning itself on. I checked the radio was off by pressing the on/off switch on the radio, went to bed and the next morning the radio was on. Once ,the battery in the car was flat. The radio came fitted with the car which is three years old and just out of warranty of course.
i have the same problem. its to do with the cd player trying to find a disc when theres not one in it, you can either pay an arm n a leg for a new one or put a cd in it to stop it :D
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Try fixfault.com to fix in-car audio.