Strange noise between 2-2.5k rpm

[zaka]

Hi all,
I've got a 3 MPS (from Switzerland), I've installed an ETS 3.25" 3 weeks ago. Now I heard a weird sound (especially in cold start) in low rpm (before 2.5k rpm) when I accelerate and decelerate. Sound like a little a bird whistle . After 2.5k rpm, it's normal noise. Then I thought that it's because of the ETS, so I went back to stock IC, stock BPV, stock intake , but the noise still there .
I've already checked boost tube, clamps etc... but no leak

Here a sound clip:

http://www.youtube.com/watch?v=wDoBcjPvrnc

Need your help!!!!

Thanks