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Discussion Starter #1
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?
 

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Are you driving on hard surfaced roads when you hear this? There is no differential between the front and rear drive shaft, so if the tires are not exactly the same size you are loading the front and rear differential as they are not turning at the same speed. This would probably be aggravated when cornering. You should only use 4wd when on muddy/ icy/snow covered roads so the wheels/differentials can operate at slightly different speeds and dissipate the load through the tires on a surface that 'gives'.
If this happens on non-hard surfaced roads, you may need to have the differential(s) checked for wear.
 

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Discussion Starter #3
It happens on any surface. I first noticed it first on gravel roads, then it persisted when I switched to 2wd when I got to pavement. Last week I used it for 30 miles or so on snow convered roads and it was very noticeable. I switched to 2wd several times in less snow covered areas and it didn't go away. Today I drove a few miles after my fluid changes with no problems, then when I put it in 4wd the problem came back immediately (dry, salty roads) and lasted a few extra minutes after switching back into 2wd. The tires are all the same size and equally worn.
 

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I'm somewhat confused. Not to repeat Old Marine. But 4wd is only for being stuck, and when you are spinning your tires. You can't flick the switch from 2wd-4wd while not stopped. This will screw up your diffs, and possibly the learning of your PCM. Try disconnecting your negative terminal on your battery for 2 minutes, and reconnecting it. This will reset the PCM hopefully. It's hard to diagnose a problem without hearing the noise your talking about. Good luck though.
 

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If you replaced your front wheel bearings with cheap ones 2 years ago, you may be ready for new ones already.


If you've been driving around with 4WD engaged at 35+MPH for any length of time, you'll be needing a new front differential.
 
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