Had the same thing on my 1990 Golf GTD! This car had the "Banzai" approach; disabeled the wastegate, blocked the pop-off on the intake manifold(YES, they have one!), IC, and adjusted the pump until it smoked BAD when revving at standstill
Oh, the car had 250.000km when this was done, still lives 100.000 later with same mods
The point is, it would make EXACTLY that POW sound when shifting gears, I liked that sound! That is, until I found out why
......it was an exhaust leak not very visible before actually driving with boost
in my case it was 20cm downstream of the turbo outlet.