It's a short video and you'll probably need to turn your volume up to hear what I'm talking about. The noise occurs as soon as punch it and the RPM goes above 2.5k. Doesn't make that noise at any other time as far as I've noticed.
It started making that noise a couple days after I added Engine Restorer do it.
That definitely sounds transmission related. Eiether that, or some kind of weird resonance in the exhaust at certain RPM's. It's very hard to nail that one down.