Bad Input Shaft Bearing?
 

After my car has been warmed up with a decently long drive, I start to notice a sound that seems like a bad bearing somewhere or something rattling. When I press the clutch and rev the engine, I don't hear it. But when I let the clutch pedal out and rev the engine I hear it, so it seems to have something to do with either the clutch or the transmission. I also hear it when I'm in gear and driving, as long as the clutch isn't pressed. What could this be? Possibly an input shaft bearing going out? Any input is appreciated and I'll add a video once I get a good one that captures the sound.

Edit: Also might be worth noting that it's MY03 with only 49,000 miles.

It could be the throwout bearing rubbing up against the pressure plate. Try adjusting the clutch pedal (give it a little more free play) and see if that free/easy adjustment fixes the issue.

in my experience throw out bearing makes a knarley squeal. Could be the very common clutch buzz.

I would have considered that, but I thought they fixed that problem by the 03 model years. I also thought that clutch buzz was mostly heard when decelerating in gear.