Help! The radio in my 1994 c280 all of a sudden has started makingsome popping noises and a high-pitch sound. This happens even when the radio is off. About a month ago I installed a JVC CD/ipod compatible radio in. All was connected properly and has been working fine. Now, all of a sudden the radio is acting weird. My mechanic said the sound is definitely from the radio as he has seen this happen with aftermarket receivers in mercedes. Does anyone know how I can fix this problem for good?

Thanks so much in advance!