Hy! My 2018 sq7 does exactly the same symptomes. Could anyone of you manage to solve the problem? After reading this thread I tried to replace the mechanical bypass valve, which is in the tube that comes from the second turbocharger. The big one that goes towards the intercoolers. The idea was that if the mechanical valve in it is damaged, the pressure which is made by the first turbo charger can go towards the second turbo charger, and finally into the air filter housing which would have explained the noise. No joy, of course.
Many of you asked The others about this bonjour Bolt thing I’m also interested in it if anyone can explain it.