When car is switched off, all bands OK but when switched on, the AM & MW bands are very fuzzy & crackling! It is a sony face-off factory installed unit. Any tips on making it clear so I can listen to these bands?
Interference from alternator? Fit a suppressor. You can get them in Halfords for a few quid. This is what I had to do with one of my saabs. After fitting suppressor no change until after a couple of minutes. I think it is some sort of capacitor.
It sounds like the supressor - I think there will probably already be one fitted... but I'm not going crawling under the bonnet at this time of night
They fit between the Live connector on the Alternator and the engine chassis (find a handy bolt!).
The way they work is to allow the AC spikes from the alternator (which is what makes the crackling/whining) to pass to the chassis. The nearer the supressor is to the alternator the more effective it is.
The other thing to check is that the ariel cable is plugged firmly into the back of the unit.. if only the central core is connecting then the ariel earth is via the car electrical negative..which will get "noisy" when the engine is started.