I just recently installed a borla catback. When I reach speeds of around 70+ my car vibrate a lot more than usual and I don't know exactly what the problem is... I really think it's due to the exhaust because i took apart the exhaust system and put bolted it back up and had no vibrations for a couple days of driving....eventually they came back...help please!

 

Sounds like it's not supported properly..

 

Shouldn't put domestic brands on rice. jk

 

How close is the exhaust to the driveshaft? Not sure how it all works on AWD, but your driveshaft could be balanced incorrectly.

 

Driveshaft could be unbalanced from all those hard awd lanches.

 

is it close to any of your suspension parts? maybe the car squats more under higher speeds or something of the sort which is causing it to hit as it gets closer. check the exhaust for smudge marks.

Maybe one of the joints is coming loose. I had a couple bolts loosen up on me before and it made all kindsa sweet music.