06 Sierra 1500 MT, weird noises in 3rd and 5th gear

[Daniel Bradbury]

Just picked up a 1-owner sierra MT with 133k. No towing package, 8ft bed, 2wd, and 4.8l motor. Owner seemed to take decent basic care of it, had motor oil always up to par and a new serpentine belt.

 

However, when I go into third or fifth, the truck sounds different. Dunno how to quite describe it; my buddy was thinking synchros but hard to tell. Drove the truck back all the way from Jax to Tallahassee, fl, doing 70/75 in 5th, and it seemed fine other than the different noise at 4th. 

 

Don't really have any trouble shifting.

Edited October 2, 2019 by Daniel Bradbury
missing info

[Gagliano7]

1st and second are the only gears with synchros. Probably a bearing in trans making a noise. Check and change tranny fluid. You have to use the correct fluid synchromesh for the manual trans. Only takes around 2 quarts.