The unfindable tapping noise

[dogfishguzzler]

Ive already done some open complaining about this so some of you knew this was coming but heres what I got.

I have a tapping/clicking noise but not at idle or higher rpms, its like low to mid range. I dont have a tach so I cant give any specifics about the range. I have a saginaw four speed (not sure about the rear end) but when Im going around 40-45; Im guessing around 1800-2200 rpms the ticking is very distinct but its not constant, its more like its on a wave or a harmonic if that makes any sense kind of in and out in a very smooth pattern or wave. I bought a stethescope and found one loose rocker which helped but today I started my truck beside a wall and I could hear it very good once I gave it a little gas. Im axious to fix this since it worries me. If Im just being paranoid that would be great but I think somethings up lol. Any insight on things to check would be killer. Thanks guys!