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Today my XC70 decided to make a new nose I have never heard before. I can't find other posts that match it. To me it kinda sounds like a chevy truck's gas pump whine. I first checked the alternator (mine occasionally whines), then the turbo control valve, and crawled around the front end to see what might be making the sound. If I pop the hood, the sound gets covered up partially by general engine noise and if I remove the cover on the engine the top end/injector sounds nearly completely obscure it. It is a constant whine that doesn't alter with engine speed, it sounds loudest over by the vacuum pump area though I'm pretty sure that isn't it seeing that the vacuum pump is engine driven and would (I think) change pitch with the engine speed. The sound isn't there as soon as I start the engine, but rather it starts shortly after and I *think* also noticed something that sounded like it briefly after I shut the car off. It is also not the HVAC motors, nor is it the cooling fans.

Below is a link of a video I tried to get the sound on, it was raining out so it kinda muffled the audio, but you can still hear it in the background.

https://www.youtube.com/watch?v=D8d-Hl5eEvU
 

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I can't hear anything in your video, but try something for me. When you hear the sound, pull your dipstick out and see if the noise goes away, & if there is a large sucking sound when you pull it out. This will indicate a failure of your oil trap (the black box on top of the cylinder head).
 

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It almost sounds like the whine/noise that many of the a/c compressors on the newer P3 cars seem to develop. Many people have the compressor replaced if under the factory warranty still, but replacing the compressor usually doesn't cure the whine as many have said that it inevitably comes back. I have the same whine from my car on occasion when the compressor is running (a/c on or defroster).
 
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