Noise when coming off and on throttle

[KernowT6]

Hi all, not sure if anyone has had similar experience, when driving with the window open when I come off the throttle in my 2017 T6 5 speed it makes a sound like a metal flap closing, when I apply the throttle again it sounds like the flap opens, could this be a drive shaft, DMF or a gearbox problem.
Any advice appreciated.