2006 TRD 4x4 Off Road Rear Diff. Grinding

My 2006 TRD Off Road has been making a low grinding noise in 2wd when the wheels are pointed straight. The sounds grows louder as the speed increases, but when going around a curve and turning the wheel, the sound disappears. My mechanic drained and replaced the fluid in the rear axle, which was very thick and smelly, but the sound has gotten even worse since I got it back.

Also, does every single TRD Off Road come with a rear E-locker? I'm beginning to think I got shafted by the used car dealer who sold it with Off Road stickers.

 

Grab your vin and put it in here it will tell you everything about your truck:
https://www.toyota.com/owners/vehicle-specification

 

Is there a button to the left of the steering wheel that says RR DIFF LOCK? Is there a power outlet in the bed?

 

Could also download the Android or iPhone app

 

Yep, after running the VIN it appears I bought a TRD sport with off road stickers. It does have an inverter in the bed, and it does not have a locker switch on the dash.

 

Yep, you definitely have a sport (just looked closer at your avatar). Anyways, good luck with your diff issue.

 

That means you have an lsd in the rear diff. Did they add friction modifier for the clutch disks for the rear diff? That would cause the chattering if it wasn't added.

 

He did add friction modifier. Right now the sound is only an annoyance, it doesn't seem to have any effect on driving

 

Have you checked front wheel bearings?

 

I haven't thought to check anything on the front axle, the sound is definitely coming from the rear diff. I've sat in the bed while a friend drove, I can very clearly hear the noise start around 15 mph and disappear when going around a turn.