I just did this mod today for $0.00 at work, before heading home. Right away I noticed a better response and enjoyed the lack of hypersensitivity of the bpv from subtle throttle changes. Seems nicer, in the brief driving I have done with it, but it REALLY changed the sounds more than I was anticipating. Also, is it normal to sound so fluttery at lower boost shifts? Its sounds mean at full boost, but is a short stutter sound at mid boost shifts, and super fluttery at lower boost. This is on my 08 wrx, with a Cobb SF intake and a OTS stage one map.
I did this mod in hopes of alleviating a subtle off throttle deceleration boost leak I have been noticing. I don't hear it when I put the stock airbox back on. It is illustrated quite well here:
A few folks with this sound fixed it by buying an aftermarket bpv or bov. I was hoping this would fix my problem, but I am still hearing it, though now at a higher rpm.