i dont know what kind of transmission you have, but i have a tremec 3550 and it makes a good amount of noise, especially in 3rd gear. when i bought the transmission, i was told it was going to make noise, and every car i have been in has made the same noises. tremecs are known for it. but its not that loud, so it probably isnt that.

but check out the u joints, that would be your best bet, like its been said already