So I just replaced the factory UIP with a Nesei hard pipe and it looks great. I took it out for a test run, and found that above 4,000rpm there is a new hissing sound coming from under the hood. The new bolts for the Nesei are on pretty tight-not super snug though-so I am not sure why there is a new sound that was not there before. The car seem to pull a little more stronger now with the hard pipe. Maybe its the BOV, but I am not sure.
Any thoughts?

 

I installed a Nisei UICP just last week ... I had a kind of whining sound coming from the engine at about 3,000 rpm. I'm not sure if it's the same issue in your case, but my problem was caused by not tightening the clamps enough. I had to use deep well sockets because the screw nut goes in quite deep.

 

hissing = boost leak most of the time

 

I think it is a leak. I need to get a deep sprocket to tighten the bolts up some more. I am not sure if the leak is from where the UIP connects to the FMIC or the other end. I can tell you though, it was a pain in the butt to tighten the bolts that connect the UIP to the FMIC. I am not sure how I am going to get to them with a bigger sprocket-