Which GFB - some (most?) of theirs come with adjustable recirculation. If it has that, and is adjusted well for it (all recirc or at least mostly), I'd be unconcerned totally.
Yes! Repeatedly and (perhaps sadly, considering how long ago that was) in person during the Group B era. Depending on the car they'd clank or screech and that, combined with the afterfire and the constant whistling that was novel at the time really added to the aura. Anyway, I digress.Ever hear compressor surge in action?