X-drive so you can disable the front? Isolation is the best way to track it down.

It sounds to me like flexing. Engine twisting on the mounts and something like a heat shield is rubbing.

You can use a microphone on an ear bud and an FFT app (they aren't free I paid $10-15 for mine just do it).

Does this only happen when shifting into and out of gear or also of you are not moving in gear and hit the gas?

My car has some drive train flex that causes an actual thump when I go from rev to fwd I think it's subframe or rear diff mounts

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)