i had to have a whole new rear screen because the radio was bad when the rear window heater was on

 

Interesting re the window change. I took my amp out following Rudy's link (thanks!), and found the contact patches on the window quite oxidised. Following a clean of these and the amp contacts the radio reception appears to have improved. It is finr with rain now, but still does not like the HRW on at all.

But if that is the only time it is unuseable i can live with that..