[2012 528i]Hich pitch sound just before turning engine off

[Chrisdot]

Hi there, would you have any idea what could be causing the high pitch sound on the video?
https://www.youtube.com/watch?v=HbLq...ature=youtu.be

It started around 6 weeks ago. Dealership has no clue, they said they couldn't replicate the problem. Problem occurs when slowing down to complete stop.

[SlackTube]

6 cylinder engine: The sound is air being sucked in through your rear main seal. As an experiment drive about 35 and come to a fast stop ( not locked up but fast ) and I'll bet the noise happens again or louder.
most of the time a new valve cover will remedy the problem as the crankcase vent system is built into the valve cover but in some cases you may need rear main seal replaced. BMW has a SIB on the noise.

4 cylinder...no idea

[Chrisdot]

It's 4 cylinder. For me personally it sounds like some belt is slipping. Could it be related to torque converter as the sound starts when car is on gear and nearly stopped and stopped?

[Chrisdot]

Also, "BMW has a SIB on the noise."; what does that mean for me?

[Chrisdot]

Anybody has an idea what could that be? Or at least how do I diagnose further?

[SlackTube]

A SIB is a Service Information Bulletin.
your vehicle does not match the SIB I was thinking of, it only effects 6 cylinder.
i have never heard that noise on an N20 engine but next time it happens open your oil cap JUST A LITTLE so you don't make a mess and see if the noise is eliminated or not

[Chrisdot]

Why oil cap? Are you expecting it could be some sort of vacuum leak?

Also, I never tried opening oil cap on running engine. I would assume it will start pissing hot oil under the hood. What you are saying, 'JUST A LITTLE' means to only turn it like 20 degrees? That way no oil should get out.

The noise happens when car is just about to stop. That car has start-stop feature turned on. Could it be that something that triggers engine to stop makes that noise?

[SlackTube]

I say open the oil cap " a little " meaning unscrew it all the way and crack it open about 1/4 inch just to let pressure/vacuum escape. Yes removing the oil cap completely will cause oil to be flung out but lifting the edge 1/4 inch won't make a mess.
I am trying to check your crankcase pressure/vacuum.
The auto start stop is called MSA and there is nothing in that system that will cause that noise.

[Chrisdot]

Here is the thing. To make it more interesting, I turned off the MSA and the noise goes away completely. In other words:
- with MSA on I have what is on the youtube video, high pitch sound that sounds like some belt slipping
- with MSA off car doesn't make that noise

[SlackTube]

That is very strange. There are no SIBS that discuss your particular situation and I have never heard that noise from an N20 much less anything to do with MSA. The only known noises on N20 engines are a high pitched whine noise similar to a hair drier noise which is the oil pump chain/sprocket but it doesn't sound like your noise.
You need to schedule an appointment to have your vehicle looked at but please keep us posted as I am extremely curious. If I had to guess Id say maybe alternator but its just a thought as I haven't heard the noise in person and its difficult to diagnoses uncommon issues over the internet.