Our Clarion CMD4 started yesterday to "plop". Every second or 2 in a steady rythm you'll hear a loud "plop". It will go louder if you turn up the music and you'll hear it on all speakers (so all amplifiers are amplifing it), expecially on the sub because it's a low frequency "plop". We turned the radio off because you can hear it, it's bad for the speakers and amp. But at the end of the day we tried it again and the display of the radio is go crazy then. It doesn't matter if the engine is on or off, or which battery is selected. Any thoughts??