I have an 08 535i n54 stock with 95k miles. Can anyone help with this whistling sound. It only comes on from about 1800rpm to maybe 2700rpm.

I’m hoping it’s something simple and not a major problem. I do feel this all started after a shop changed my valve cover gasket maybe 2 years ago. The car has been using oil since and the whistling sound was mild at first, more so when cold, but recently has gotten much worse.

 

Check for a vacuum leak. Do a smoke test or the spray soapy water trick.

 

Thank you! I'm going to take this into the shop that did my Valve Cover, and I called and confirmed they have a smoker to do a Vacuum leak test. Hopefully it some simple plastic part that's worn out.

 

Hoses can become very brittle over time and are easy to damage while in the area.

 

Question, will a SMOKE test work with the car idling and get pulled into the Turbo system? The car is cleary making the noise when accelerating and the Turbos are pulling Boost. Wasn't sure exactly what kind of pressure or air flow goes through the turbo system if the car is no accelerating. Wasn't sure if I need a shop that has a Dyno or something to actually test it as the car is "Simulated" driving under load.

 

Do what you stated above. ^^

 

Heading in Thursday morning. Also noticing power is WAY reduced now, no turbo boost just whistling. I’ll report back!

 

Sounds an awful lot like a generic loose hose situation...

 

Aren't you getting 30FF underboost codes? Check engine light on?

 

So, bad news....
No Codes..
Smoke tested, there was a Hose that failed the smoke test, it was kind of under near the air intake on front right of engine bay (While standing facing the engine), I think it's called Turbo Bypass Valve and Hose or something, replaced it, test drove.. same thing. Seems the sound is NOT a whistling, but more of a Whinning. And boost feels very LOW and it ONLY Comes on with Boost. Seems to be 1 or 2 bad turbos or a bearing in the turbo fan or something of that nature.. I think I'm going to move on from this car unless someone has a better idea. I don't know how we inspect the turbos without tearing down a bunch of stuff to get to it and not sure i want to sink more into that.

I'm open to suggestions. I'm guessing retail pricing on turbo install (new turbos + Install is upwards of 8-10k.