What would cause 2nd gear whine from take off trans is a nv4500

Low fluid... 2nd gear issues, bad gear. Any metal in the oil?

No metal that I’ve seen 

Whine is usually something misaligned, whether it's just a lot of use on that gear or something has shifted.

4th gear in my 5600 started whining a few weeks before it stuck in 4th. Got it out but would not go back in. Not sure what was wrong, I replaced the tranny.