Could be a loose clip or hangar with the exhaust....also, I would check underneath the car for loose retention pins/bolts, brackets loose...experienced a lot of that with my 06 and 11.I hear it when i start the car and when im driving in a parking lot uphill. Is this normal? Im not sure if i had this before or if it started after i installed my Corsa exhaust. Should i take it back to my muffler shop?
Edit: I drive a 6MT GT PP
Do you by chance have video of the noise or know of a similar video with the noise prevalent? I have a automatic 2015 GT, and it makes a noise that I think is similar to your description, but when I asked the dealer to check for the flex pipe, they said there was nothing wrong. I don't trust them very much and want to figure out what the exact issue. I can send you my video of the noise I have, if that's any help? Any input from anybody would be greatly appreciated.Found the source of the vibrating noise! It was the flex pipe right after the passenger side catalytic converter.
My shop told me to try the dealership before going to a muffler shop and hacking up the exhaust. Im thinking the dealer wont approve the repair since i installed the exhaust already. I cant put my stock exhaust and take it because i had to cut it for it to fit in the car. What do you guys think? Don't even try?