SLK radio locked up
 

Repeated from SLK forum
Just purchased a used SLK. The radio worked fine this morning but now the radio is set on the station last used and plays fine. The problem is with the radio controls. Every button is non functional, including the on/off. If I press any button the radio goes dead for a second and I hear a beep then the radio resumes operation. The beep does not sound like it is coming from the radio, but from behind the dash on the drivers side.

Ok, so I pulled fuse for the radio and then restarted the radio and entered the security code. All was well. About 3 hrs later the same thing happens, all the buttons are dead. Repeated the fuse pull and restarted. Now ever key enters a 9 in the security code. It seems really screwed up.
Any thoughts?