Weird noise on acceleration (low speeds 20-40 mph)

I have been hearing a weird noise kind of like a flappping noise on acceleration as low speeds. When i let off the accelerator and coast at the low speeds (20-40) it stops. So assuming it is the transmission, what could be wrong?

any help?


http://rapidshare.com/files/415187970/Voice0002.amr.mp3

most noticeable sound is from bout 2-9 seconds.

anybody?