I have the sat nav unit and for some reason my radio keeps going abit crackly like im losing signal its ok when i flick to another channel and back but then it going abit fuzzy again .
karl iv heard this before and yes its most likely to be your rear heated window causing interference.
Try your radio with the heater off and see if this makes any difference.The trouble is the aerial for our cars is the top line on the rear window that looks like your heater but its not.
This is for the saloon the tourer aerial is on the small rear side window from memory.