I was also having other whistling sounds and I thought it might be coming from my A/C tensioner, so I replaced it at the same time. Now I have no kind of sounds at all. For those still complaining of a whistling sound, check your A/C tensioner. Its easy to get to from under the car and is literally a 10 minute DIY max.
Also, on my intake there are 2 hoses coming off a connector on the main tube of the intake. While working on this DIY, the smaller hose cracked. It was not a big deal and I replaced it with another hose I had laying around but what was it for? I know its a vacuum line of some kind.
Also, my SES light just came on after this DIY and a 200 mile drive.
TRS 5000K XB Bi-Xenons | ümmitza 6000K Opaque AEs | Metallic Tinting | LED Interior Lights
^2001 E46 325i^ SOLD
Current: 2013 SEL 2.5 Jetta 5MT
2010 E90 335i M Sport in Le Mans Blue