Grinding noise from drivetrain - update

[Adoomie Abdallah]

After taking my truck to several garages and no one could pinpoint my problem I decided to just do trial and error. 

 

The noise that I hear sounds like a grinding with different severity of the sound. It only happens under load / acceleration and happens randomly. when I let go of the gas it stops when I press the gas again it will come back it sounds like it's coming from underneath middle/rear. Also when the grind noise happens, the RPMs go up slightly, and when it stops they drop again. (transmission/transfercase issue maybe?) 

 

First I removed the front drive shaft and took it for a test drive the noise still persisted. I put the front drive shaft back and removed the rear drive shaft and took it for a test drive, the sound went away. 

 

I started at the rear diff I took it apart cleaned it put in all new bearings checked pinion and gears for wear and they were good, as well as the contact pattern was good. Put everything back together, same sound. 

 

Drive shaft is good, u joints etc. So I ruled out the entire back end. What would you do next for diagnosing the sound? 

 

 

[rav3]

I'm just guessing over the internet & guess it may be your transmission torque converter. How many miles? Pull transmission dip stick & see if you see any sparkles on it

[BO TIE 1]

If you have or know anyone with a Go pro camera attach it under the truck and see if you can pin point it. 

[rlcole321]

If you are sure the sound is not there when you disable the rear drive train, which sound like you do, then that really rules out the trans/TC, so it points to the Transfer Case, have you check the fluid in it for Debree?