Help Me Identify This Sound

LinPark

I don't have a video of it (yet - I hope one isn't necesarry) but hopefully describing it will lead someone to the answer. I just got finished installing Berk HFC's this past weekend and previously I had put in Stillen G3's the week before. At wide open throttle I start to hear a high pitched scream (almost like a whistle) as the car heads into the 4k+ RPM range. I don't remember hearing that when it was just the Stillen G3's installed but it is definitely there now that the Berk's are in place. It doesn't seem to happen when the car is just sitting and rev'ing but only under true acceleration. Any thoughts on what this might be and whether or not it is just a normal behavior of this particular combination? I have the HKS Hi-Power exhaust as well. I did dismantle the G3's to install the Berk's - is there an easy way to detect small leaks on the intakes or cats?

Thanks!