Very loud, high pitched sound coming from engine bay (N55)

**MozartE90** · 05-24-2020, 12:26 PM

Hey, everyone!

I bought my E90 3 months ago and finally got around to installing an aftermarket downpipe last night. It was pretty tough and took me about 10 hours (lol). I let it run for a while and tried to check for leaks before leaving the shop, did a test drive, went back, let it run for a bit longer. Everything looked and sounded good as far as I could tell. Of course, as soon as I start driving home I start hearing this: EARFUCK WARNING! https://youtu.be/3hrt61FqzW0. (Ignore the chirping in the background; those are crickets lol). I honestly thought it was some kind of siren coming from the nearby airport at first.

From my research, the only videos I could find with similar sounds seemed to be diagnosed as failing PCV systems. Is it possible that the increased flow from the new downpipe caused the PCV system to fail?

I went out today and tried to re-create the issue but it didn't occur during the 15 minute drive. Maybe it didn't reach operating temp, idk.

Anyone have any further knowledge of this issue?

**jclausen** · 05-24-2020, 01:01 PM

When it's making the sound loosen the oil cap if it was pcv related the noise should change or go away

**MozartE90** · 05-24-2020, 02:01 PM

Thanks for the reply. I'm going to try that when I'm able to replicate the issue. Is PCV noise usually something that comes and goes? I just drove for 20 minutes straight and no sound came up.

**JDStrickland** · 05-24-2020, 08:04 PM

N55,m so 335. You messed with the exhaust not far from the turbo. The noise went away, so maybe it was a one-off kind of thing. But the sound seems like a dry bearing, that kind of thing. It would suck if the turbo locked up.

**MozartE90** · 05-24-2020, 08:18 PM

As far as I can tell the car feels pretty much the same as it did before. I drove it a lot today and didn't have any issues. The sound was so loud that I'm surprised it isn't something that's popping back up.

**JDStrickland** · 05-24-2020, 08:29 PM

Originally Posted by MozartE90

As far as I can tell the car feels pretty much the same as it did before. I drove it a lot today and didn't have any issues. The sound was so loud that I'm surprised it isn't something that's popping back up.

I agree, it's a noise that should pop up again. Crossing fingers.... Hoping for the one-off event.