Hi all, something the cars always done, but ive never gotten around to asking why..

2001 Wrx (bugeye)

When it starts boosting, it seems fine, but once the car gets to about 4000 rpm or higher, the suction noise from the pod seems to just go quiet and I can barely hear it at all. It doesn't seem to lose power though.
The car only has a diff back and Pod filter (I know a pod alone isn't worth having, but I like the noise..)

Any suggestions?