I have an 04' dakota 4x4 with the 4.7L. I noticed over the past few months that there is a humming/whining sound when driving in 4high. It is loudest at about 35 mph and does not change when I shift to neutral at that speed. It does not seem to be tied to load on the engine or RPM, but rather just speed. It also feels like there's a little extra drag. It stays for several minutes when I switch it back to 2WD. After a while, it will go away and will drive normally in 2WD. About a year ago I replaced the front hubs/bearings. Within the past 2 years I have also done the tie rods and ball joints. The tires are the same as they've been for a long time with even wear. Because of the sound I just replaced the front diff fluid, transfer case fluid and topped off the rear diff fluid (It was just changed 2 years ago). I pulled and tugged on every drive shaft, U joint and CV joint I could find and didn't find anything loose. All the rubber boots are in good shape. My guess is that something in the transfer case is dragging. Any other suggestions before I give up and take it in?

 

In 4 wheel drive, there is going to be more driveline drag. Just the nature of the beast. I also expect a bit of noise, simply because there are a bunch more parts in play. If you are driving on a 'marginal' traction surface, it will likely be even noisier. (patchy snow on the road, or such like)

 

Thanks for the response. I've had this truck 6 years now and use 4wd regularly, so I'm used to how it typically is. These symptoms are all new over the past few months.

 

It's possible that something is too tight, either the grease dried out, or simply outlived its useful life. Given that it is speed sensitive, and not load sensitive, I would be looking at the front driveshaft. Maybe drop it out, and move things around by hand. See if something isn't hanging up/binding in there. Since the problem isn't present in 2wd, it's gotta be either the front shaft, or the t-case itself.