Might be a stone, Ian. This gave my car a problem pushing it, along with a rear brake that wasn't coming off correctly - and various noises that came and went (but then there are lots of different noises, of course).
Thanks for the picture Tim. I removed the rear plastic cover again and checked the belt and teeth for stones. Nothing obvious. Pushing it in and out of the garage in neutral eventually stopped the noise but later on a test drive it returned. Initially I thought it was related to the brake drum/handbrake. I've sent a copy of the recording to Allon White with the hope they can identify what's going on.
My belt sounds exactly the same it squeaks slightly but Rtcc have set it up exactly as they say is perfect but I have never had a clunk like that?? Sounds like the prop shaft or something hitting alloy plate but listening on a video is never good.Plus I am daft ;-)