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Today, my 2008 BMW 323i started making an unusual sound when I accelerate. I've owned it for less than a week, so I'm not very familiar with what the engine should sound like, but it drastically changed today.

I drove 5 minutes to an auto parts store to buy a new turn signal bulb and washer fluid, and the engine sounded totally normal.

I filled the washer fluid reservoir and replaced the bulb, and then when I was driving home, almost immediately the engine sounded really weird, like it's wheezing or having a hard time breathing.

At first I thought I maybe spilled some washer fluid on something, but there doesn't really seem to be much around that area that I can see.

A few specific things to note:

  • the sound happens even when I'm in neutral and just putting my foot down on the gas pedal, and does not need to be moving to get the noise
  • the noise doesn't seem to happen while it's idling, but

Here is a video of the engine running, and you can easily hear the sound while it revs up: https://www.youtube.com/watch?v=H8o_RqQ6WDY

I've been googling and watching youtube videos about these BMWs with whirring sounds, but I haven't been totally sure if it was the same sound, since the audio quality of most videos is pretty bad, especially while driving.

Has anyone heard this before? It will be a few days at least before I can get into a shop.

UPDATE Nov 19: I brought it into a BMW specialist and they showed me that there's an area under the engine cover where oil is leaking, and said there's definitely something weird going on in the engine. Will update again once I find out what it actually is!

  • I don't know what that sound is, but it doesn't sound normal. I suspect it's a bearing as it rises in pitch with engine RPM, I couldn't say which one though. – GdD Nov 16 '20 at 11:14
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Remove your fan belt(s). Start engine briefly to see if noise disappeared. If it did check all pulleys until you find the bad accessory. Replace bad part and put a new belt(s) on if necessary.

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The belt should not squeak at idle, as can be heard in the video. It may be worn or stretched. Spray silicone spray lubricant on the ribbed side of the belt while the engine is idling (be careful not to get anything caught in the belt). If the noise disappears for a time, have the belt replaced. If the noise does not disappear, follow the instructions from Jupiter.

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