When driving in low range, I get a whining sound as the rpm approaches 2k. I usually don't hear it much at slower speeds, but when driving about 20mph, it sounded like this

The diff lock doesn't seem to change anything. I was told the noise is normal, but to me it sounds a little excessive. Is anything wrong?

 

Oh boy that is not what we thought you meant at the time. Have you checked the fluid level/quality?

 

Fluid level is good. It was a darker brown color, but not black.

 

When was the last time you changed it? Any shavings?

 

my transfer case made that whine - ended up replacing it and no more whine

 

I have never changed it, but I assume (hope) it was changed when the transmission was swapped about 10k miles ago.

 

Do you have any idea what was wrong with it? I would rather just replace a smaller component than the whole thing.

 

I would suggest draining and replacing the gear oil in the transfer case,you have no idea what is in there or what it is in. You should also check both diffs

 

Why are You driving 20mph in low range?

 

I sometimes go more than 20 mph in low range. There’s a lake that I frequently go to where the “road” in has a lot of sections where you need to be at a crawl and a lot of sections where I can go over 20. I don’t think it’s necessary to keep changing between low and high range.