Bill,
This is funny, I had a pretty good puff off yesterday on a trial run for the fun of it. Thankfully, my lid works well, too. I caught part of it visually, but the noise is like a big rattle You can see it here; at about 1m42s. I ran my only running engine, my 8 hp B&S. Revisited leaving the vac(fan) running while starting the engine. Some quizzical looks from me, I’m sure.
Pepe