Need help diagnosing shifting noise

2001 Tacoma 3.4L V6 4WD Double Cab TRD Off-Road with tranmission cooler and towing package.

Started hearing a 'clunk' sound when I shift from 'P' to 'R' or 'D' and back and forth, especially when the truck is cold first thing in the morning. Also 'groans', perhaps rubber? Right now I'm thinking a u-joint and maybe the center bearing on the rear drive-shaft. When I put the transfer case in 'N', the transmission shifts very smoothly with no sounds at all. So, I am thinking the transmission is fine; am I wrong to think so? Also, after driving a short distance, the 'clunk' sound is not as pronounced but still there, and there is no 'groaning' sound. The truck drives find with no noticeable vibration but it does howl like loud tire noise, again making me think u-joint and center bearing. If I put the transmission in 'N' while driving down the Interstate, the howling continues.

I'm not sure how the relationship between the transfer case (which shifts well enough from 4H into 'N' and 4L and back again) and the transmission works. I wouldn't think the 'clunk' is coming from the transfer case. I'm hoping it isn't the tranny, xfer, or rear diff.

I did change out the fluids in the front/rear diffs and xfer case, and I also greased the 10 zerks on the drive shaft. I have not changed the tranny fluid for some time and it is due.

Any advice would be helpful. As of now, I'm thinking about taking the rear driveshaft off and inspecting it closer. It does have 300K on it and never had any u-joints or bearing replaced.

 

With 300k the carrier bearing is almost certainly toast.

I'd suggest that both the clunk and groan are consistent with a bad carrier bearing, u joint, or more likely both.

 

Also worth checking the transmission mount while down there. If it ain't been replaced in 300k, it's probably also toast.

Edit: it's also insanely easy and quick to replace.

 

Can anyone help, 2011 tacoma 189,000 miles, when I turn truck on and press gas panel all the way the engine sounds great and does not stalls but stalls when I drive. hope to hear from someone. Thanks

 

Wrong place.
Try here:
https://www.tacomaworld.com/forums/2nd-gen-tacomas-2005-2015.5/