Loud undercarriage rattle under load

[S]

Cant locate where its coming from. Assuming drivetrain since its only on acceleration. usually light accel. mostly on an incline. Rattle stops once foot is off gas. 

1 shop spent 2 hours on it. Said it could be bad drive shaft? Not sure why that could be. Said unjoints all looked/felt solid. 

Heat shields all snug.

Will not rattle when on lift. Seems to only happen when all tires on ground. 

Happens both 2wd/4wd. And tow mode. 

Shifts in an out fine. Rear diff fluid changed. 

 

Longer it goes on more i dont trust driving but need truck for work. 

 

Any help

Edited September 21, 2021 by S

[S]

[S]

[richard wysong]

did you pull the driveshaft to check the ujoints? sounds like you may have 1 frozen that a shake test won't show

[S]

That i have not yet attempted. 

 

If it was locked up wouldnt the rattle be more persistent? Or it's just a certain torque that the rattle kicks in and out. 

[rlcole321]

try putting the jack stands under the rear axle and putting it in gear to see if something is out-of-"round"

[S]

Unfortunately already did that. Ran it through its gears few times. Nothing sounded off. Dropping off at another garage in hopes they can find this

[richard wysong]

Ive seen them just chatter under light acceleration and be quiet otherwise. an experienced tech will know the sound. could be in the transfer also. there is a multi channel remote listening device that some shops use to diagnose wheel bearing noise etc.'  its easy to drop the driveshaft . should only take 10 min on a lift to eliminate that possibility

[S]

Shop on thursday said they feel its the transfer case. Taking it to a transmission shop this friday for second opinion. 

 

Said same thing i told them. Noise cant be duplicated on the lift. felt that since its only noise underload then signs point to the tc and not the tranny. They also told me to drive it till rattle becomes more consistent instead of just throwing money at parts to get a sure diagnosis. 

[S]

Had rear passenger upper shock bolt weld come loose. Welded back up.  No more rattle.