Here is a more recent video that he just sent me.
Definitely hear something that is not the usual sound. Considering it's on one side, could it be something as simple as a tiny exhaust leak? I know I chased a strange (and freaking annoying) noise on my gasser once and it ended up being a TINY leak at one of the exhaust ports where it met the stock manifold. Several "good" mechanics couldn't figure it out. Even with a gasket, it took having the mating surface machined flat to cure the leak.