Any differential experts here?

[RenoHuskerDu]

Do the small lines on these satellite gears merit concern?  It's a Sterling 10.5" diff

I'm chasing a wonga wonga wonga noise from the diff above about 40mph on smooth pavement.  The R&P are in great shape, no pinion play, and it's not running hot. Only had 110F today on the pumpkin, and 76F on the wheel bearings. Ambient was about 55F. Carrier bearing is only a couple years old, it and U-joints all good.

Oil was a little dark but not much metal dust in there. I'm adding friction modifier tomorrow, didn't have any on hand when I opened the diff today.  This truck is tuned to about 450hp and occasionally does tow heavy, so sometimes there is heavy load, like when I find a nice Bully in a farmer's field and go tow it home. But generally she's my daily when not driving a heavier work truck or dump truck.

[mat in tn]

I would check the differential carrier bearings, but you might check tires also

[RenoHuskerDu]

mat in tn wrote

I would check the differential carrier bearings, but you might check tires also

The carrier bearing is surely a possible cause. But when I spin the wheels at 60 mph up on jack stands, the sound seems to be directly in the bed over the diff.  And that carrier bearing is recent. We replaced it along with the big U strap that it lives in. It passes a shake and pull inspection.  But you're right, that could be it.

As for tires, that I eliminated possibility by running the truck in the air.  

[mat in tn]

actually, I read the post a couple times to be sure of what you had already checked.  I saw that you checked the carrier bearing on the drive shaft. but the differential rides in a pair of carrier bearings also. four in total at the "chunk" itself. two roller type at the sides where axles intersect and then the two for, and aft on the pinion. any one of these four could do this. however, the two on the sides will sound slower than the two on the pinion, so if you hear a sound, the way I understood then my gut says carrier bearings. the spider gears are along for the ride in an off the ground test and should have been silent.

[Maurice]

Any chance you could try one of those stethoscope with a stick things or hose on it? Without wrapping yourself around the driveshaft or wheels, of course.