Strange driveline noise

I've got a sound coming from somewhere in the driveline and maybe y'all can help me find and fix it. To start my truck is an unmodified '11 off-road with around 119K miles. The sound changes when going from accelerating to slowing. It's sort of a whir that doesn't change pitch with speed. If you put the transmission into neutral while coasting the noise goes away. There are no noticeable vibrations.

It has been gradually getting louder where now it's starting to bug me. Suggestions what to look at?

 

OK, the problem is fixed. If the internet points you here this is what I did.

First I changed the oil in my diffs and transfer case. TLDR: Maybe ran a little smoother, but no change in the whirring sound. I changed it with full synthetic at 60K miles so I was due for another 60K change. The oil I put in at 60K miles was clear. When the rear diff was drained it was pretty dark. Not black, but I didn't feel bad about changing it. The front diff was a little dark, but I'd say it had a lot more miles left in it. The transfer case was almost perfectly clear, I'll probably let it go to a 100K before changing it again.


Second I replaced the center carrier bearing. TLDR: Wow did that make a difference. The noise is gone, but so are the vibrations. I didn't know I had vibrations until they were gone. It's like a whole new truck, well worth the cost of the bearing. The dealer quoted me $600 to replace it. A quality after market bearing is $60. A few hours of work and I had an extra $540 in my pocket. Tip if you're DIY in your driveway, use a ratchet strap to keep the drive shaft from falling on you and to hold it up while aligning the bolts. Also, beating on the diff and transfer case flanges with a hammer will get you nowhere. There are notches on both flanges, just take a big screw driver and pry them apart.

 

Is there a DIY guide in the forums on how to replace the center carrier bearing?

 

Not sure what year your truck is. But this is the DIY from the 1st Gen forum
https://www.tacomaworld.com/threads/how-to-replacing-carrier-bearing.260283/

 

There are dozens of videos on youtube. I'd say its a 3 out of 5 difficulty. Mostly because the flange bolts are tight. If you have an air gun its a 2/5.