VW PD Diesel Sports Exhaust Fitted - Strange noise

Given the vast amount of topics and information I can see on this site, I'm sure this has been answered before but I just cannot find it anywhere..

On a VW PD TDi engine, when a "straight through" or sports exhaust like Milltek etc. is fitted, these cars make a strange noise when coming off throttle under boost...sounds like "poooooooo" I cant describe it any other way, sorry!

Is this the wastegate or the turbo stalling? Or something else?

Many thanks guys

Not a good description of the noise. I have 3" all the way back and mine makes no such noise.

Well, there's no wastegate on the turbo so it's not that. I think I know the noise you're talking about, and I'm pretty sure it's just the turbo slowing down.

Mine sounds like this now:

http://pics.tdiclub.com/showgallery.php?cat=4114&ppuser=36337

it IS just the turbo slowing down. mine does it quite loudly even when I'm hardly on the throttle, but the cool thing is that it scares the crap out of people on sidewalks.