My '91 wagon is experiencing a problem with the radio. There is a terrible noise when the radio is on and the noise gets worse when I operate anything electric (eg, the turn signals or the power windows). I've replaced the radio noise supressor relay and that wasn't the problem!

I was told it might be a ground problem. I did recently replace a faulty antenna motor, but everything was fine for about two months. Since this is the only thing that has changed, it might be the problem. What should I look for to "run this to ground?"

Thanks