I've had a nagging whine for the last several years that happens at highway speeds. It's audible only when the accelerator is depressed. The noise can be feathered on and off really easily with a corresponding feathering of the throttle on and off. It sounds like it's coming from the transfer case. Is the rear output bearing a strong suspect?

 

Sorry, I can't help but I just drove mine today on the highway and I have a light whine/whistle too with acceleration around 65-70mph (I can also feather it on/off with accel/decel.). Previously I thought it was the front driveshaft (or possibly the roof rack and lights) but I've since greased that so I doubt it's that. Interested to find out if you discover the cause.

BTW, I previously had a bad T-case in another DII I owned and whine was significant at all speeds.

 

I also have that issue but only happens above 120km/h it's been doing it for the past 12k kms, but never at lower speeds so I'm also interested in the solution

 

My 04 also has had a similar whine for as long as I've had it

 

TC gear whine is somewhat normal. Can get worse if fluid is low. Maybe try different weight gear oil, or high viscosity additive to see if it changes its tune.

 

My 2004 was dead silent by comparison, so I know it's not just a characteristic of the transfer case. All indicators point to a bad bearing. Front or rear, not sure, I'm just going to replace both. I ordered all the parts necessary to change them. Should be here next week. Will report back in a couple weeks after they're in whether or not the issue is resolved.

Gave me a fun excuse to get some beefy ratcheting Knipex snap ring pliers