Nato

Hi folks, hoping someone has run into something similar. I've got a mystery squeak that's very intermittent I've been having a hard time tracking down. It's a 2010 535xi. I've already replaced the serpentine tensioner, belt, and idler pulleys. I managed to get a recording of the squeak here (it only squeaks the first couple seconds):
There was one time over the summer I got the squeak to happen when the AC was turned on, then it went away when I turned the AC off, but since that day the squeak seems totally random. It seems to be a little worse when it's hot. Sometimes it runs without making any noise, and it'll squeak once when turning the engine off. Sometimes it'll squeak once or twice when parking right before I turn the engine off.

I'm thinking it might be the AC compressor bearing, but it's so intermittent it's hard to pin down.

Thanks for any help!

Nato

Just a follow-up if anyone else has something similar. The PCV valve was not functioning correctly, causing excessive crankcase vacuum, which caused air to be sucked in through the rear main seal. Popped a new pcv valve on and the chirp is gone. I think it may have caused some damage to the rear main seal, but I'll keep an eye on it and see what happens.

spazzz

Thanks for the follow up.

NoQuarter

That is a weird sound for sure.

Your follow up is great!