Searching For A Squeak

My car has developed an interesting squeak somewhere indefinable.

I returned from the hairdresser's* to find Mr Flum taking the wheels off to check the brakes, but so far has found nothing amiss.

Perhaps we have a mouse nesting in the boot (obviously not in the silencer...).

*and a second visit to the Christian Aid booksale at Holy Corner - counting the George Street one, that's three piles of 'new' books.