Noise when 2003 VW jetta diesel is running?

Whether or not the car has the engine running, I hear a constant ticking sound coming from all the speakers. And only when the radio is on. I had suggestions on checking the spark plugs but this is a diesel. I also got a suggestion on chcking for a bad ground and I will be doing that. But I was wondering if anybody else has encountered something like this before or has any more suggestions that would help in troubleshooting.