Only with foot on brake, is it a miss fire or drop in rev as it may try and creep forward but can't as the brake is on so the revs fluctuate? Not an auto driver so only a question.
Whooshing would probably be pressured side of the turbo. Only takes a small hole. There is a weak point somewhere that I've seen mentioned on here, a elbow joint that might even be plastic
While a joint is ok, I'm not sure a reputable garage would use one. By the time the joint was made a complete pipe could be installed. A pain on axle stands to get in but probably easier on a ramp.