I would still suspect the baffle. It might not be loose, but may be disturbing the exhaust flow just right.

I have another question. In the video, when you open the throttle, it sounds and acts like it is terribly lean. The engine is not revving up, it just seems to change tone to "blat, blat, blat" without much change in rpm. Was the engine cold when you made the video? It sounds like a cold engine with no enrichment (choke).