front diff. problem??

Hi all, I have a 2000 tundra 4x4 with a problem in the front diff. The truck has a humming sound that comes from the bottom of the truck when you drive it. The 4wd works ,but I checked the axle shafts and they are pretty sloppy in the front diff. Long story short I pulled the front diff. thinking the brgs. are bad ,but I cannot find any play in the brgs.Any suggestions?? Thanks,, By the way the diff. was very low in oil!!