Found this product that reduced the whine noise in my transfer case. With high miles, poor service history, I went with 85W150 synthetic several months back. That helped, but still had some whine. Read a post about ZF transmission rebuilding, and how one company made a special additive that really was more than snake oil. Figuring that Higgs Bosun had plenty of time on the transmission bench, I looked up the product. Made by Lubegard, and they have a whole family of products. Central premise is it is a replacement for oil made from sperm whales.

See LUBEGARD Gear Fluid Supplement

I put about 7 ounces of the Gear treatment in my transfer case and went for a drive. Whine almost inaudible now, certainly below tire noise. Now my ears are not a sharp as some, wayward youth wasted on rock music; and my Disco transfer case is not identical to the next one, and my tires are not same as yours, and my exhaust leak needs attention. But for something that is less than $10 at NAPA, and you could swap out at next transfer case drain, why not?

BTW - they also make a product for automatic transmissions, and I used that in SWMBO Kia (212K) - quieted tranny down, even though I use synthetic fluid.

Thanks, Higgs.

GOOD info, I think I'll give it a try

its the same stuff you use in the posi drivetrain. We call it whalesperm cause thats what it use to be made out of. no longer.

Yes, they originally thought that, but it came from a large organ in the head of the whale which some believe to be part of his echo location system. Was used in cosmetics, lubricants, etc.