Just out of interest, do you know when the bearings were last replaced? Smooth is subjective if turning the wheels with your hands established said smoothness as they could be just staring to fail. They may not be that smooth with the car resting on the wheels in addition to cornering forces. If you can't see any obvious rubbing & the wheels aren't knocking when rocking them (indicating bearing failure) then I'd wait a little bit to see if the sound gets worse - if it does & you can't see anything obvious again I'd check the bearings.
I'd tend to agree with Phil regarding the steering pump noise. As for CV joints though, I replaced mine (at 75k miles) after I'd lowered the car as soon afterwards I started getting a vibration/rumbling sound on acceleration from stop or hard roll-on, both in a straight line, obviously highlighted due to the lowering of the vehicle which had changed the geometry. This failing was totally different to the bearings which generally only made a noise when turning (until they got that bad it was at all times).
The front bearings had been renewed 24k miles previously (at 51k miles) so I could somewhat confidently rule them out. I ended up replacing both drive shafts c/w CV joints with salvaged ones as a cheap diagnosis (£45 for both sides in 2011) & it fixed the rumbling. On inspection of my old ones the CV joints were rotten.
As I said though, this was a much more agressive rumbling than a "simple" hum/rub that I'd expect from an initial bearing failure sound.
Somewhat difficult one to nail down without seeing and/or driving the vehicle as Richard's findings turned out totally different but somewhat self-inflicted is my guess
Good luck