2018 JLU Sport clicking noise when decelerating

[Cjbelfiore78]

Hey everyone - Have a 2018 JLU Sport with 35,000 miles, manual transmission. When decelerating and RPMs are around 1000 (typically happens in 3rd gear, but can happen in any) there is fast paced clicking noise. The noise is more in sync with RPM speed than wheel speed. Mechanic took off rear drive shaft and drove the Jeep and the noise still occurred. Had thought might be drive shaft. Has anyone experienced this? Also, we replaced rear differential fluid b/c it was black. Going to take off differential cover and take a look in there Monday. Any ideas what could be?
thanks

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[Heimkehr]

@Cjbelfiore78
Welcome to the forum.

Just spitballing here:

I had an almost identical, speed-sensitive clicking occur on a K1500 that I used to own.
Turns out, the original u-joint on the rear shaft was dry and required replacement. Chevrolet couldn't be bothered to spend an additional 10 cents per unit, if even that much, to spec a zerk on their u-joints.

One Dana Spicer greaseable fitting and $80 of labor later, and all was well again.

As written, your post suggests that the mechanic engaged 4WD so as to drive the Jeep in front-wheel drive, since the rear shaft had been removed. Might want to have a look at the front driveshaft and differential, then, to confirm the state of their health.