Train horn noise when in 4wd

[GingerKid]

We finally got enough snow that I had to use my 4wd around here, and it's making noises on me. It doesn't start immediately, but after a few minutes driving at a decent speed (~40mph), my truck suddenly starts sounding like a train horn. The noise will only go away if I come to a complete stop. It also only makes the noise when in 4wd. I can drive with the hubs locked and in 2wd no problem though. I'm going to check fluid levels tomorrow when I get a chance, any other ideas on what could be wrong?

 

[srteach]

This loud hum could come from anything that only moves when in 4WD, while under torque. Check u-joints in driveline for need of grease, check oil level and cleanliness in the front diff. Let us know if you find anything.

 

[costeve]

Hey man - I am having a VERY Similar issue - Any way you could post what you found!? I am giong to be under mine from tomorrow evening until I figure this crap out!

We finally got enough snow that I had to use my 4wd around here, and it's making noises on me. It doesn't start immediately, but after a few minutes driving at a decent speed (~40mph), my truck suddenly starts sounding like a train horn. The noise will only go away if I come to a complete stop. It also only makes the noise when in 4wd. I can drive with the hubs locked and in 2wd no problem though. I'm going to check fluid levels tomorrow when I get a chance, any other ideas on what could be wrong?

 

[mattpresley]

y'all need to quit wheeling nears railroad tracks

 

[GingerKid]

I actually haven't had a chance to look at it yet. I've been busy between work and school and it was a low priority since I can run it fine it 2wd. I'm guessing it's something transfer case related since it didn't make the noise in 2wd with the hubs locked in.