Are you sure it's coming from the underside of the car and not the engine bay?Looking for some guidance here.
In Sport Mode, with a a 6 spd, when decelerating in 2nd or 3rd by letting the gas off, there is a metal flapping noise (3 or 4 times) coming from the rear underside of the car. It only happens in Sport Mode but is consistent. It sounds like something is loose or not connected.
Do others have this as well?
If it's coming from the engine bay it could be your air intake. If not seated correctly, when you let go of the accelerator something like the air filter could be moving when the suction is released... or something along those lines... It's a bit of a stab in the dark but the clue is that you can replicate it when you release the throttle