Help me identify this sound/vibration issue

pixologics

TJ Enthusiast
Joined
Jan 26, 2021
Messages
209
Location
CA
Hi guys, I've had recently upgraded the rear driveshaft u-joints which we found had some foul play and it about 50% of weird noises that were coming while driving at speeds above 20mph.
I'm still observing somewhat similar noise pattern at speeds above 50mph. I've inspected the front driveshaft u-joints and they seem to fine and I dont see any movements in them while I tried to hold and shake it.
Today I while I was driving downhill at speed of 45mph (3rd gear) I noticed same vibration even while I was not pressing gas pedal. To see if the noise reduces I put it in neutral and I observed that the noise reduced drastically.
So, what part is that I should be looking for replacing to get rid of this noise? Any tips.

Jeep Wrangler TJ 1998 Sahara 4x4 4.0L 6 cyl. Manual transmission. 31" tries with no lift.