I just got a boost drop problem fixed a few months ago. It was the C-clip on the waste gate arm under the heat shield. A bump may pop off that C-clip leaving the arm to tap on the turbo or the heat shield.
Everyone was telling me to get a boost leak test. That is just what we were about to do when we removed the heat shield and there it was.
Just a wild guess.
The sensation is as hard to forget as it is to ignore!!!