Sounds normal to me. Mine does the same thing!Here is a video of the noise
Yep, that Kubota UDT2 is good stuff. Worth the extra dollars for sure.I know this is a little late in the discussion, but with my Kubota BX-23D I changed the hydro/transmission oil and used standard udt rather than synthetic. After the oil change my transmission began to whine more than normal. I changed back to the udt2 synthetic and the whine decreased greatly.