I only heard it (beacuse it is so low sound) when I'm parked (red light and such) but I'll try and rev to see what happens then. I only heard that same sound, and it hasn't changed in pitch at all.
I did a search and this guy had what I think could be somethign similar, and that was the power steering fluid resevoir that needed to be topped off
http://986forum.com/forums/general-discussions/28107-04-2-7-tiptronic-whining-noise.html
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