Since I changed the gearbox oil in my LT95 it has developed what I can only really describe as a sort of mechanical growly noise. It only does it after it's warmed up, wasn't there before I changed the oil. Which was surprising as when I drained it I only got about 2.5 litres total out both the gear and transfer box parts. I refilled via the fill level holes on the sides with 20/50 mineral oil so there's definitely the right amount in there.

Is it worth trying a thicker oil or maybe just a better branded one? Or is it just acceptable that these gearboxes are just agriculturally noisy, all the gears still work OK.

Just to update. I don't know if you sorted this but I'm about to do the same myself and from what I have researched it's supposed to be 20/50 in the main gearbox and EP 80/90 in the transfer box so maybe the fact that you used 20/50 in the transfer box has caused the growl....

Hope this helps.

IIRC, LT95 use ATF DEXRON II not EP80 or 90.