I have a 2006 B2630 and it squeals every winter. I have noticed that it only happens when the tractor is in motion. Therefor indicating transmission and like yours will stop once the tractor warms up. I am using UDT but my dealer recommended it for this climate. I have also noticed that the noise gets louder as the RPM's increase.
Thanks a lot everybody for the information. It puts my mind at ease. The dealer told me that he has never had a hydrolic pump go bad on a Kubota and will stand behind it and he is so confident will cover it even after warranty.