Anyone ever heard this before? My daughter’s 2011 XC90 3.2AWD started making this noise yesterday. It also threw the Check Engine light, producing a P0171 and P0174 a day before. It’s most evident at idle, both in gear and out of gear, doesn’t change if it’s in drive or reverse, and seems to go away under acceleration. This video is right as she turned off the engine… Thoughts? Maybe a vacuum leak? Pitch seems too high and squeaky - should be more of a sucking sound if it’s a vacuum leak - but would coincide with symptoms of the codes it threw. Doesn’t emanate from under the hood either; it’s most prominent under the driver’s side door. Input is appreciated!

 

And FWIW - the vehicle runs fine; No knocking, no rough idle, no obvious power loss, but then again I haven’t pushed it hard since the Check Engine light came on. I pulled the codes with my code reader and reset the CE light, but it came back on almost immediately.

 

Another data point; pulled the MAF sensor to see if it needed cleaning, (one of the suggested fixes for the P0171/74 codes) but it was clean as a whistle.

Ran the car briefly yesterday and didn’t hear the sound again. Seems to come and go.

 

After a little more research I discovered that this whistle is the result of a failed PCV membrane. Video illustrates that the whistle goes away when pulling the dipstick.

So I bought a new membrane and cover and replaced it today. Whistle is gone and so is the Check Engine light and codes.

In my research I found that people just break the cover to remove it. I opted to cut it as pictured with a dremel cut-off disk... Came right off without issue. I only cut the 3 I could see near the front of the cover. Rotating the cover and pulling up on it released the rear catches. Oh - I also removed the whole PCV assembly first so I could remove the membrane on a workbench instead of reaching over the engine. Cleaned everything up and put the new cover on, but found that it doesn't stay in place...not sure why. I threw a little adhesive on it at each of the three front tabs. I figure if I ever need to replace it again,I'm going to be cutting it off anyway, so the adhesive won't matter.


Cut cover with a dremel...

Underside of membrane/cap.

Before cleaning.

Typical split membrane.

Cleaned up

New membrane and cap

Installed.