Noise In 2wd, Not In 4x4 2009 FX4

[AGrayEngineering]

Alright Guys, After owning a 88 XLT, 98 XLT, I though I'd be problem free for awhile after buying my 09 FX4 new. Well I was wrong.

Background:
09 FX4
37,000 (go figure I'm only 1k out of the bumper to bumper warranty)
5 spd man

I'd say the problem started a few weeks ago, I noticed that there is a slight rattle in the drive-line. It's most notable with the windows down between 15-40 mph, any faster and I cant hear it over the wind. The funny part is when I engage the 4x4 it goes away. My gut says (and I hope) it's a problem in the u joints, but I grabbed the front shaft and it seemed tight. I've cycled it through 4H and 4L a couple times hoping if it were hung up in the t-case it'd loosen up. It's not an awkwardly loud or even a bad noise. It's just not normal and annoying. I can't imagine that with only 37k on her that the parts are shot that quick, but you can't rule anything out. Its only been wheeled 3 times and never anything hard, mainly just getting out to the hunting grounds. I'll try to check this shafts this weekend but I was hoping I could get everyone input.

 

[amarillo06]

On our trucks 06-and up... The front axle still rolls the driveshaft and into the transfer. There could also be a bad Propshaft on the transfer case end of the front driveshaft. Jack it up. And spin a tire. See if the sound is there with no power against it. Mine was making noise in the prop area of the driveshaft. Also check the transfer case fluid level. Just a couple things I've found in chasing rattles and squeaks under mine. (134k on it)

 

[AGrayEngineering]

Thanks for the response. I took it to the dealer & they replaced one of the axle shafts & the noise went away.