I'm having trouble finding the source of a whistling (not whoosing) noise after I installed an M2 airbox. I installed intake hard pipes at the same time. Basically it makes a whistling noise at -250mm to -300mm. The noise is similar to air blowing by jelousies (?sp) in a high apartment building. So, it only does this under light throttle. Boost pattern is perfect, there is no whistling/whoosing under boost.

I sealed all the edges of the box with silicon sealer and made sure all clamps are tightened down.

So far I can only think of two things it could be, my primary turbo hard pipe is not perfectly aligned with the airbox (1/8 inch off). I dont think this should matter because the coupling seals the connection.

Also, I looked at the airbox, and the hose connection on the box on the upper right hand side of the box has a small hole (~2mm). In other words, the hose connects to the airbox, but the inlet is very small. I was wondering what the reason/function of this is, and if its possible it could be causing the whistling noise.

 

I get that sound too, once my car is warm. Still haven't figured it out. Perfect boost pattern. I guess it's just a side effect of getting rid of all the restrictive crap. It also restricts noise.