I've got a problem with my car stereo .. or should that be ICE these days ??

Anyway, it's a 2005 Nissan Primera - nothing flash, I'd rather spend my money on other things.
The damned thing has always made a weird metallic scraping or buzzing noise intermittently on MW.
I listen to talkSPORT and 5Live for the football chat and match commentary and it is so bloody annoying.

It's a strange noise that is made worse by holes in the road, changes of gear (it's an auto, but you know what I mean) or braking, so I wonder if it's some kind of issue with grounding or something connected to the body of the car somehow ?

The other curious thing about it is that the interference/buzzing/scraping sound changes pitch depending where I am on the dial.
What I mean by that is talkSPORT is a completely different tone to 5Live, while the three separate tuning spots for talkSPORT (1053/1089/1107 in my area) all have a different pitch too.

I've never had this issue in any other vehicle.
Crap reception : of course, this is MW after all, but never this odd accompaniment.

Anyone got any ideas ?