Whine at specific RPMs

[MattB]

Tonight while driving my '01 I30 I noticed a new noise. At somewhere between 1500-2500 RPMs (hard to tell exactly where, as it comes and goes very quickly) there is a noise that sounds half way in between a whine and a rumble. It sounds like it's coming from the passenger side front (maybe the wheel). Above 2500RPM the car sounds just like it should. The car pulls strongly, shifts properly, and otherwise drives exactly as it should. It also recently had a 90K service which included flushing the engine and transmission. Anyone have any ideas what this could be?

[MattB]

To clarify, it seems to happen only at 2000RPMs or so. Above or below, no noise. It's as if there's some kind of resonance.