Took it back to the shop - the pipes were vibrating against the darned cross-member. They added in spacers to lower the cross-member and the vibrating sound went away.

Driving back from the dealership was awesome. The exhaust sounds so clean and throaty down low and it barks like a Porsche up high. Total driving bliss.

Thanks Ark!! :)

Push up the Y pipe as high as you can before you bolt it down. It helped with mine