Originally Posted by Angus Brown
It sounds to me like the lash isn't properly set. If it's too loose or too tight, it will whine or howl, depending on which it is. The fact that you can hear gear mesh is what's giving it away to me at least.
The only other thing I can thing of to check outside of the differential would be the transmission mount to see if it's separated. For giggles you could unbolt the u-joint caps where it's bolted up to the pinion yoke and rotate it 180 degrees and bolt it back up. You can get weird drivetrain vibration if the point where two yokes are connected aren't put back in line with how they were when taken apart, since driveshafts are balanced, but I really doubt that's the problem, it or a separated transmission mount wouldn't produce gear whine.
Can you take it to another shop for a second opinion?
Thanks for the response. I don't think it has anything to do with the drive shaft as this is the second shaft and u-joints with (exactly) the same issue..the first one was stock, and the one on there now is a cv shaft. Transmission/tc mount was replaced right after I did the lift due to separation so it's less than a year old and I've had the skid plate off in the last two months and it was fine. It might not be exactly gear whine that I'm hearing, but could also be bearing whine. The shop that did the work does tons of wranglers, and they were very willing to open it up again and check it, as well as pull the drive shaft and road test it a couple of times...and all for free. And because I can get it to do it at lower speeds by gearing down, I no longer think it's coming from the difs.
I've been driving it like this for almost a year, but I tend to stay below 60 on the freeway so I don'thave to deal with it, and it hasn't gotten any worse or better. I'll probably just keep using it until I pull the trans for the clutch job...who knows, maybe I'll stumble on the cause.