took a video if the induction noise in my TDI, it gives you a fair idea to just how crazy it really is, and I drive it real quiet in carparks and other public enclosed spaces ( it's a bit embarassing at my age ), but I'm certain there's a lot less restriction between the intake and the engine than VW delivered it with!
The filter I am using made a lot of difference to the induction noise, as it has an open front design.
Induction noise video:
I've gone back to a K&N oiled one, as I was finding some fine dust in the intake from the Apexi, even though I've been swapping them out at about 30k's. I'd rather possible MAF issues from the oil over dust chewing out the poor TDI's innards.