[Ernest72]

Originally Posted by Varelco

The reason those flaps exist is to equalize the air pressure inside the car. If you seal these you are in theory sealing the car (assuming the windows are up). It doesn't help the HVAC pump and circulate air inside the cabin. They also act like a pressure relief when you slam those doors shut. So yeah, don't block them, they are there for a reason, not to mention blocking them will do nothing. Sound isn't like water, it doesn't just seep in through gaps, it vibrates through the entire car.

Your exhaust is resonating at a very low frequency, unless you intend to fill the cabin with masses of material sound deadening will do very little. The 2 solutions you have are to replace the exhaust or have a helmholtz resonator fitted in your exhaust (this will be particularly big for low frequency)

helmholz will be done. I did not seal them just stuck some foam down there. it did nothing. this car is just too tinny.