Exhaust rattle

MaQG37

I don't own a 370 , but a G37 that shares the same test pipes/HFC as you guys. I thought I'd post here since the userbase with aftermarket exhausts is much greater than the g37 forums.

I recently installed resonated test pipes to an Invidia Q300 catback. Hiss was there, but expected. However, I just switched to a Stillen catback that has a Y-pipe utilizing a slip joint on one side. I am now getting a metal on metal rattle at 1800-2000 RPM. I checked the U-clamp that tightened the slip joint. I used a stethoscope to hear for any potential leaks around the slip joint and nothing. I've removed any heat shields that could possible even touch the piping, nothing.

Any ideas? I've stumped 2 local exhaust shops already.

Link to Video.