Hey guys,
So this is my first transmission rebuild and I'm trying to narrow down what went wrong.

I have a y1 transmission ( small spline cable b16 ) that I recently rebuilt with the master carbon rebuild kit from synchrotech.
The kit included all the bearings, seals, synchros and slider hubs and i also bought diff bearings too and replaced them too.
While I was in there I swapped the mainshaft and countershaft 5th gears from a small spline b18 ls transmission I had ( s1 i think )

I went to test drive the car and it shifts great through all the gears but there is a whine specifically while coasting in 5th.
The whine goes away when you give it any gas or clutch in.
It whines a little bit through all the gears, but it had a lsd in it when I bought it which I couldn't find a name on when I opened it up so I associated it to that.

There are a few things that I think I could've messed up - I didn't get new needle bearings for the gears on the shafts but i picked the best one i had out of 3 transmissions.
I also checked the thrust play and it was ..001 and from my understanding the thrust play doesn't matter as much for ball bearings as they do the tapered roller style, but i could've taken an inaccurate measurement.
I also think the transmission may have been run low or without oil that i rebuilt but it didn't seem bad when I got into it plus the 5th gears I put in were good for sure

If anyone has any insight on what could've gone wrong it'd be greatly appreciated!