4x4 low

whats up everyone,
Sorry I couldn't find a 4x4 thread to post in so hopefully I'm posting in the right spot. Yesterday I was in some deep sandy loam going uphill to a fishing spot. I switched from 4x4 hi to 4x4 low to crawl through it because I was starting to get stuck. When I made the swap I noticed a humming coming from the front diff. Once I crawled out I stayed in low and the humming stayed the same. Is this normal? Just a light hum that came from the front end and the higher the rpm the higher the humming. I don't know hopefully it's normal ???

EDIT: the hum only occurs when I'm on the gas. No humming at a standstill

 

May just be gear reduction noise from the transfer case. Kind of tricky to say what it is without being there to hear it.