I had exactly the same problem as clubscene last week.

I went to disconnect the amp under the spare wheel as he suggested but some further online research suggests that the amp is actually under the DVD ROM drive on the left had side of the boot. It's apparently the radio tuner module that's under the spare wheel.

Anyway, to cut long story short I disconnected 30amp fuse No 72 on right hand side of the boot and replaced it and all is well!

Everything back working with sound (TV Sat Nav, Bluetooth & Radio) and no settings lost