I think it's between 45 mins and 90 mins that it happens. I never get the W in normal use at home, and only in the car during bumpy stretches of road).

I'll try it again tonight a) with the lid off b) with the player in standby c) both of those, and report back.

The whine I mentioned does sound exactly like a drive spinning down - is there a hijack timeout for this that I can configure?