Hey Crice, do you any experience with the prefilter? I was listening as close as possible with my sis tapping the gas and I'm pretty sure I isolated that hissing sound coming from down where the filter is. It could be the silicone coupling, clamps or filter but its definitely down in that area. The reason I ask is that the prefilter feels and sounds like that cheap-swooshie pants, wind breaker material. The type of material that would make that sound. I have a hunch it could just be the air getting sucked through that. It's definitely down in the filter area, an area I can't see directly into, all the hoses and seals up at the top of the intake/throttle body are tight and sealed.
Jus figured I'd suggest that in case you did have the prefilter and yours doesn't make that sound. I could rule that out. If not then I'm gonna have to remove splash guard and take a good look at that end.