Yeah - I've thought about swapping BPV's to see if that makes a difference.

And, yep, the volume and behavior of the whistle varies GREATLY from car to car... I've heard others that were "quiet" - but mine was NOT quiet... it was LOUD... you could hear it any time at partial throttle around 2500-3000 RPM, windows up and top up with my open CAI installed... or with NO intake or hose installed...

But, like I said, now I have nice performance AND nice sound AND no whistle... all good. Unless you want a car that sounds like a lawn mower or a weed eater or a chipper shredder - mine doesn't sound like any of those...

 

I have an 04 MCS with a MM CAI and my wife has an 06 MCSc with a MM CAI and they both whistle. I really don't see how that whistling is that bothersome. Actually, I didn't even know I had a whistle until my wife told me, now I can only hear it in her MINI.

The only reason I put CAIs on our MINIs was for ear bling, not for HP. I LOVE that whine and that is why we got CAIs.

 

I just put the Alta intake on mine this weekend and the noise from the throttle body at partial throttle was intolerable (I've rode in others with this intake and it wasn't nearly as loud, but I think it greatly depends on your throttle body). I took the stock plastic piece for the back of the air box and drilled about 6 inch or so wide holes in the back of it to let it breathe more and put it back on and it is remarkably better. You can hear it still, but not nearly as bad and you can certainly still hear the supercharger whine. This is to me a good comprimise in performance and driveability. Hope that helps, as this thread helped me come up with this solution! Thanks,

 

I would like to thank the original poster for this thread. For the last two months I've been trying to figure out what this sound was and feared an eminent breakdown. Now I see there is nothing to worry about.

In addition to other comments, I think that temperature density has something to do with how loud the whistle sound is.