1999 Blazer 4x4. Getting a loud rhythmic roaring noise from the rear of the vehicle when accelerating. Goes away when I let off the gas.

I took it to a shop thinking it was U-joints but they said all of them were good. Fluid levels in xfer case and diffs are fine.

Recently had issues with the Transfer Case Control Module that caused it to shift into 4WD Low and stay there. It's my sons truck and he drove it for several days wondering why it was so slow. (he's never had a 4WD before and the 4WD button lights have never worked so he didn't know).

I fixed that issue by replacing the TCCM with one off EBay for $99 bucks thanks to finding that bit of info here on this forum.

I'm resigned to the fact the transfer case may have been damaged by driving it for days on the road in 4WD low but we were hearing this roar before the TCCM issue but not as loud.

Any thoughts?

 

How does the fluid look in the transfer case? Rear axle?

If you sit in the back seat and listen to the noise does it sound like it is under or slightly in front of you (transfer case) or behind you (rear end)?

 

I took it to a quick lube place for a scheduled oil change and had them check the xfer and diffs fluids. They said they were fine. I'll do the rear seat test and report back.

Thanks.

 

Definitely coming from the rear. Called a local shop and described everything and he thinks it might be the pinion gear. Gonna bring it to him and let him take a look.