Holy cow Ginseng, did you ever find the solution to this? I thought for sure it wasn't my downpipe hitting the firewall (the clearance is huge), but these are the EXACT symptoms I have to the T so far. Does it also make the noise if you take off from a standstill?
https://www.youtube.com/watch?v=Zjro...Vh-R-i-3RL6PCQ