not sure if it is a belt slipping, my intake hissing (i removed the front scoop part and connected a tube out the bottom down to the ground, plus have K&N drop in filter). but anyways, from about 5000 rpms up there is a hissing/sqealing noise. more towards the hissing side, but i'm not sure. just wondering if anyone else has this problem. oh i only notice it in 2nd gear at WOT, 1st gear blows by too fast i think for me to notice it love the 2k2 acceleration. thanks all

 

Normally, you hear hissing/whislting with aftermarket intakes.
But I could be wrong and you might be experiencing a vaccum leak..

 

I've heard that sound on occasion and my car is stock. It's just the air being sucked in the intake. I only hear it in certain places when the audio dynamics are just right. Since you've modded your intake, I'd suppose it's even louder now. It kinda sounds a little like a turbo.

 

I hear the same thing on my car. Sounds like a turbo spooling. It sounds like it's coming from the passenger side of the car though. When I have friends that sit there, they notice it's louder on their side.