Hey guys, have a very strange noise under the hood for a week now. Car is Civic EX '01 with 100,000 km on it, and is 5 spd. Noise appears only between 2k and 3.5k rpm in all gears when I try to accelerate fast (to pass), but if I just rev in neutral - it's not there. For slow acceleration - I can't hear it. Any thoughts?
Thanks a bunch.

 

Forgot to tell - this is noise is sort of metal tapping sound.