Rhythmic knocking

[Mstrunk7]

I cannot figure this out I have been racking my brain. About two weeks ago I started hearing a metalic knocking. It only happens when I let off the gas and cruise. It turns into a hum when I go back on the gas.
View: https://youtube.com/shorts/SkbjfgQ8rLU?is=YkelRb1QV6RrpJRv . It sounded like it was coming from the middle or rear of the rig so I started by taking off the rear drive shaft and driving in 4 wheel drive. The sound went away. So I figured it was the u joints. They didn't seem to have much play so i replaced them and the sound was still there. I have checked all my controll arm bushings and they seem fine. There doesn't seem to be any up down or in and out play in the differential pinion yoke so i dont think the pinion is bad. My next step is to check the transfer case. There didn't seem to be any play in the slip yoke so im not sure if it's the output shaft bearing.
(fyi I do not have a slip yoke eliminator, and it has a 3 inch lift. I know I need to change it but it has been like this for a while and only started making this noise recently)

I will also drain it and check to see if the chain has stretched. But if that shows nothing I dont know what to do next. Does anyone have any idea because I feel like I am going crazy.

 

[JMT]

I cannot figure this out I have been racking my brain. About two weeks ago I started hearing a metalic knocking. It only happens when I let off the gas and cruise. It turns into a hum when I go back on the gas.
View: %5BURL%5Dhttps://youtube.com/shorts/SkbjfgQ8rLU?is=YkelRb1QV6RrpJRv[/URL] . It sounded like it was coming from the middle or rear of the rig so I started by taking off the rear drive shaft and driving in 4 wheel drive. The sound went away. So I figured it was the u joints. They didn't seem to have much play so i replaced them and the sound was still there. I have checked all my controll arm bushings and they seem fine. There doesn't seem to be any up down or in and out play in the differential pinion yoke so i dont think the pinion is bad. My next step is to check the transfer case. There didn't seem to be any play in the slip yoke so im not sure if it's the output shaft bearing.
(fyi I do not have a slip yoke eliminator, and it has a 3 inch lift. I know I need to change it but it has been like this for a while and only started making this noise recently)

I will also drain it and check to see if the chain has stretched. But if that shows nothing I dont know what to do next. Does anyone have any idea because I feel like I am going crazy.

You might lower the TCase skid 1” and see if it goes away. If so it’s not happy operating at that angle.

 

[Mstrunk7]

You might lower the TCase skid 1” and see if it goes away. If so it’s not happy operating at that angle.

I can give that a try but it just seems weird that this lift has been on there a long time and only now decides to make this noise?

 

[TheBoogieman]

Throughout all of my TJs and Jeeps over the years I have found out that if you have an issue that you can't pinpoint, ask a guy named @mrblaine that knows everything IMO. If he doesn't know what it is, you're screwed and subjected to internet opinions.
p.s. If you don't like honesty, avoid him.