Transmission & Differential - Transmission noise?

I have a 97 Civic EX with 70K miles. There is a strange noise that appears to be coming from the transmission. Only happens in 1st through 3rd gears. Every now and then you can hear it in fourth. The best way I can describe the noise is it sounds like a playing card in the spoke of a bicycle wheel. I only happens when accelerating and the noise gets faster as the car accelerates which is what leads me to believe its in the trans. When decelerating it goes away or when pushing in the clutch. Raised front of vehicle and drove through the gears but could not duplicate the noise without a load on the vehicle. Any help would be greatly appreciated.

Something to try:

The throwout bearing is a floating bearing. When the car is in gear and driving down the road the T/O bearing is just sitting there riding on the input shaft housing of the tranny. Try placing very little pressure on the clutch pedal while you are accelerating. You want just enough pressure to make the T/O bearing TOUCH the pressure plate but not disengage the tranny. If the noise goes away, then you know that it is your T/O bearing causing the noise. This does not however mean that the T/O bearing is bad. You may just have a weak return spring on the fork.