Just put about 600 miles on the car over the weekend, and it drove flawlessly. Started it up this morning, and noticed a growl from the exhaust, right under the front passenger side. Assumed it was the connection from the header to the cat; I've had this before. To my surprise, it wasn't. Then proceeded to check the entire exhaust system for leaks, it's completely leak free. Tightened the bolts from the turbo to header pipe and the bolt from the transmission bracket to the header pipe. All vibration-free. Yet there's a distinct growl accompanied by what sounds like exhaust shaking at cold startup & when accelerating. At warm idle the car is silent, at cruising speeds you can barely hear the exhaust.

I'm really stumped by this one. Anyone experienced something similar?