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.