Sorry Michael - I don't have an answer, but I have exactly the same problem with a Citroen. Have you managed to solve yours yet? So far I've tried several radios, replacement coax cables and aerials, a suppressor on the alternator, bonnet and radio earthed separately and a rubber belt hanging off the back of the car to try and minimise static - in case that was what was causing the problem. Nothing's worked - was going to try a booster aerial but it doesn't sound like that helped you much, so I just wondered whether you'd got an answer to your problem yet??
Ruth
August 2009