So I'm trying out a dry flow filter (thanks dthdcrd). Excuse the cardboard, it's just for measurement

As expected, the turbo and air flow are louder, but when I shut the engine off, I hear this sound as its spooling down:
http://youtu.be/bL2BmYvFW7USounds a little more friction-like than I would expect. When I recently had my head gasket, TB, WP replaced, and ARPs put in, the guy mentioned that the turbo looked great and was most likely replaced by the previous owner. Bought it with ~30k and now I'm at 94k. I've always heard air rushing noise when shutting the engine off. Just seems different and maybe shorter than I remember.
I see no oil leaks and oil level is normal.
Is this a normal sound?
Thanks,
Aras