Radio reception (again!)

[Fox]

I appreciate this topic has been done to death, but I seem to have a strange variation on the theme. I have a newish Kenwood radio/cd player fitted by PO that works fine as a cd player and usb device reader. However, at some point the radio reception went on the blink. Assuming the aerial amplifier under the spoiler is at fault, I stopped using the radio.

Imagine my shock then as I was driving along, for my mp3 play list to be loudly and clearly interrupted by a BBC traffic news bulletin. This despite the unit refusing to pick up a single station when scanning - just lots of white noise.

HTF???

I know the aerial is embedded in the rear side screen, so does the amp just boost VHF band or does it work across all bands?

I've checked all connections, but there is no logical explanation as to why the traffic news section of a BBC local radio should come through loud and clear - including the few seconds of Music program after before all goes silent again. The unit spends most of its time on standby.

Is there a multimeter test I can perform on the amp unit under the spoiler?