Clicking noise in 3rd gear (Manual transmission)

[masospaghetti]

I just finished my head install, took the truck to the car wash, and on the way back it started making a loud clicking noise in 3rd gear only. It doesn't sound good.

I assume this means something internal to the transmission is bad? Anything else it could be? I just rebuilt the transmission less than 500 miles ago.

 

[rasouth]

Does the noise happen as you are shifting into gear or all the time while driving?

 

[masospaghetti]

While driving in 3rd gear when power is being applied. It's quiet in all other gears, and it's quiet in 3rd gear while coasting.

 

[MrQ]

Is hard to shift into third? Me thinks it may be synchros.

 

[masospaghetti]

Shifts into third just fine.

 

[masospaghetti]

Decided to go ahead and pull the tranny (again), this is what I found when I drained the oil - 3rd gear seems to have lost a tooth:

 

[masospaghetti]

Any suggestions for why a gear would lose a tooth like this?