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Volvo s40 2007 - High-pitch whiny/whistling sound from under hood. Cause? Link of recording attached

Two days ago, after driving my 2007 s40 t5 (about 80K miles) for about 1.5 hrs (highway), a high-pitched whiny/whistling sound started from under the hood. The noise occurs when the car is in motion and when parked. Note the link below contains a recording of the noise.

Any thoughts/ideas on what could be the cause? Thanks.

Sound recordings like that are always hard to decipher. Did you happen to pop the hood to try to find the general area of the sound?

Check your power steering fluid.

Sounds like an old Star Trek phaser or maybe it was the tricorder to me.

@picklehead, sounds like balance wheel

Start the engine, pop the hood, stick your head under, have a friend rev the motor, and see if you can tell from where it originates.

If your serpentine belt(s), often called drive belts and sometimes even fan belts, are original, there’s a good chance they’re due. If they show signs of cracking and/or glazing (shiny spots), they’re definitely due. But let the sound lead you.

Post back with the results. We do care.

@mountainbike is spot on with his assessment. The only thing that I would add is to use a piece of water hose to help narrow the search.


+1 to doing some basic detective work under the hood in order to try to trace the location that the noise is emanating from.

However, a BIG caveat is to make sure that you don’t have anything like…a scarf…a necktie…long hair…jewelry…or anything else…dangling when you bend over a running engine.

I dropped the car off at a local Volvo service center and they think “its a known issue” with regard to the PCV breather box. The center will only be able to work on the car next week, so I’ll keep you guys posted on whether the problem was in fact due to the PCV breather box. Thanks for the help!!!

Here’s an update:

I just got the car back from the Volvo service center this afternoon and am pleased to announce the noise has gone away, although note I only drove the car for roughly 5-6 city miles. The following was replaced: “PCV Oil Trap and Ventilation Hose,” “hose clamp”, “cable tie,” “cable tie,” “sealing ring,” “hose clamp,” " oil filter hou[sick]", “Hose.” Also, the parts fell under the extended warranty.

Thank you all for the advice!