Turbo noise

Sorry if this is a repost.. but I recently got the MPPK for my 435i 6MT and every time I let of the throttle in 1st and 2nd gears I get a high pitched "whoosh" sound from the engine bay.. sort of like the sound from a blow off valve (I know we don't have one). Is this normal? I drove a stock 435i auto a few weeks ago and there was no whoosh sound at all.



Thanks