A "gear noise"--what is it?

[SailorKane]

I am getting a noise, like a whine, that appears to be in the drive train somewhere. It varies with speed. No noise at rest. Its not a wheel bearing (they've been replaced). It has been pretty quiet, but getting a bit louder. What's the most likely source of the noise? I'm wondering if transmission, u-joints, differential? Not sure of the location of the noise, but it appears to be more from up front, rather than the rear. Any thoughts?

 

[Lube]

U-joints don't whine. They'll squeal or clunk, but not whine. When was the last time you checked the oil level in the rear end?

 

[SoNic67]

Rear differential might be low on oil, leaking... Luckly you have only one to check on your 2WD.
If is not that one and it comes from front, it might be gears inside the transmission. Check that one for leaks, fluid level (read the manual how to do it right).