2005 Civic, MT, 120k

Last week the car developed a humming noise coming from the front. The pitch changes depending on how fast I'm going, it acts/sounds a lot like tread noise but it's not the tires.

Noise does not change when I turn. Wheels are firm and don't wiggle at all so the wheel bearings seem ok.

I put the car on jack stands, took the tires off, started the car and started going through the gears. Sound is exactly the same as when I'm driving.

Now here is where it gets kinda weird. With the car on jack stands I hear the hum just fine in the cabin, however I cannot hear the humming noise when I'm outside. Not to say its not there, the engine may be drowning it out. With the car idling in 5th gear (about 20mph, when the sound usually starts) I sat right next to the tranny and couldn't hear it, the tranny did not sound smooth though, I could hear the gears moving, not sure if that's normal.

So....any ideas?