It was without oil, it now produces very less noise, I
perhaps have to do more maintenance. 

----- ORIGINAL MESSAGE FOLLOWS -----

Is the noise the same in every gear and the pitch relative
to the engine speed?  If so you probably have mismatch ring
and pinion or out of adjustment.  When manufactured these
gears (spiral bevel gears)were not only sold as a set but
they were matched tooth for tooth then lapped together like
the valves in your top end.  I have had that problem with Kj
ears and now have a gear lapping machine that should not
only mate the gears through the lapping process but also
find the relationship to each other that runs the quitest. 
just a thought.
----- ORIGINAL MESSAGE FOLLOWS -----

You may have a mismatched set of gears. 
Noisy, whining trans typically are used gears from 2
different engines

R


My
noise is a whirring, when it turns to the least one,