My 88 240DL's buzzer will not shut off. Initially, the buzzer operated normally, except that it began sounding whenever I turned on the radio. At the same time, I noticed that all the radio presets and also the analog clock went out whenever the ignition was switched to the off position. Recently, the clock has died completely, and the buzzer sounds constantly. I'm wondering if the ignition is reading the key's position correctly, as occasionally the buzzer will continue after the key is removed; I've had success in silencing it in that situation by reinserting the key until I hear a tumbler(?) click. That usually does the trick. Any ideas would be most appreciated.