Not too serious. When I filled the transmission WHILE WARM AND ENGINE RUNNING, it took another 1-1.5 quarts. But it still makes this whine. I am planning to put 75w140 synthetic into both diffs, and Dextron III into the transfer case just to try to rule those things out.
Bonus question. I'm also confused about cooling system not releasing pressure overnight. Last time I wanted to check coolant level, I opened the reservoir COLD, some pressure was released and then the reservior FILLED. I thought that was weird.