I've had my V70 for nearly two years which is almost as long as I have been puzzling over a whistling sound coming from somewhere in front of the firewall. When the car is cold...and especially during colder months...I get a high-pitched whistle that subsides if and only if I move the steering wheel to one side or the other, and it resumes when the wheel is stationary again. Despite my best googling powers and a mechanic's stethoscope I have yet to confirm a diagnosis. The most plausible explanation I can come up with is that it's something in the PS pump itself. Maybe the relief valve whistles when idle and stops when there is a demand for fluid? Or is this a symptom of the pump just plain wearing out?

I know these cars had an early problem with hoses flaking and crapping-up the filter in the PS reservoir, but mine looks good. No flakes, and no unusual sounds when I actually turn the wheel. (I hear a faint hint of a "whoosh" when holding a long corner. My last car had electric PS so I forget if that's normal. Steering effort feels completely reasonable.)

One last strange thing: the PS fluid (Pentosin) smells like popcorn. Heavily buttered. My can of fresh CHF-11S doesn't really smell like anything so I have to believe that means something.

Any ideas?

TIA
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2009 V70 3.2, loaded...with dogs.

No the noise is NOT normal. If it smells like anything, flush it sooner than later. If this car is used, the prior owner might have added some strange fluid, so it is best to flush and know what it is.
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My back feels better when I sit in a Volvo seat

Thanks. I'm reasonably confident that it has the correct fluid (green as it should be and records indicate that the car had been dealer-maintained) but a proper flush is probably in order. I have wondered if that smell is due to overheating. This is just more speculation, but could a faulty or fouled relief valve cause excessive pressure and overheating? (And noise?) I'm not familiar enough with the design of the valve to know if that's plausible. Is that something that I could inspect prior to flushing?

**EDIT** Relief valve, not check valve.

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2009 V70 3.2, loaded...with dogs.

I am unaware of any check valve in the PS system and have never heard a PS system whistle.
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My back feels better when I sit in a Volvo seat

Ahh...sorry, I see my mistake. I meant relief valve (to allow fluid to recirculate while there is no demand) not check valve.

Either way I appreciate your input. The advice to flush seems sound. I had previously tried "refreshing" the fluid by repeatedly draining and refilling the reservoir at ~1wk intervals, but of course that isn't the same thing.
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2009 V70 3.2, loaded...with dogs.

Bleeding the PS fluid was pretty simple for my friend. We idled the engine and let the PS fluid come out of the return hose (top of reservoir) and when the pump nearly empty and gurgling (still lubricated inside)switched off engine and refilled the reservoir with the fluid (green for my '99) and worked it thru system briefly. No air bubbles and has been two months good steering so far.