5th gear occilating vibration/drumming

afternoon all,
I've just completed the installation of a 1.22 t/fer box into my 110.. Prior to the change I had play in the front output bearing which meant it rumbled a fair bit. Now the rumble/vibes etc from that are gone I've now found a new issue (which I think was masked before)...
at 60mph in 4th.. no vibes/runs smooth. Same speed in 5th I get an occilating vibration/rumbling noise through the floor/seat... it does change with road speed (but not directly related to speed) and it goes away if the clutch is pushed or if you change down to 4th... so it appears to be 5th gear related.
Before I panic.. I've checked wheel bearings, prop UJ's, t/fer box output bearings and diff inputs..other than a potentially knackered 5th gear is there anything else I should check?

Cheers, J

r380?most likely rear most layshaft bearing ,unlesss you find anything else id get it fixed quick otherwise gear box will be scrap

Lt77... but I had the same fear.. I'm guessing to do the layshaft bearing it means box out? or can you get at it from the top?

they dont have a bearing in th rear case ,and lf was layshaft bearings it should show in 3rd as well ,but 5th gear is probably worn,sometimes you can catch them in time and get cheaper repair

hmm.. any way to confirm this? Or anything else to check for issues before I have to "whip" the box out and get it reconned?

its difficult sometimes even when you know what your listening for,often shows up in oil ,you can drop t/box sump and check for play in bearings (intermediate gear can be adjusted easily )if its just related to 5th gear then probably gear box as if t/box it you shoiuld be able to go fast enough in 4th for it to occur

Had a chat today with a local landy guy who I've always trusted and he suggested running the gearbox through the revs/gears with the t/fer box in neutral to see if the problem showed.. (either noise or vibes)... niether showed. Which made us both wonder if it could indeed be further down the drive train.
Guess I'm back to removing props and double checking my earlier thoughts.