My '92 5-spd with 152k was making the same kind of noise, and only quiet in 4th...I didn't have any of the popping out of gear problems though. I took mine in to get fixed, and it was the main bearing at the head of the tranny...sorry I can't be more specific...the guy showed it to me and that's what he called it. I had it in to have the top end redone, and to have a new clutch put in, so it was all apart anyway.