Is This Normal Front Diff Behavior?

It was really late and I was already really frustrated when I got started, so I know I wasn't thinking clearly.  I also haven't really screwed around with 4MATIC or other AWD systems that much.  Help me understand what I'm seeing here.

The GL350 started making a pretty noticable hum last weekend.  I did about 600 highway miles with the trailer and when I was coming off the highway I heard this noise that could best be described as a growl.  It's directly correlated with road speed, introduces a touch of vibration or a feeling of roughness into the steering wheel, and goes away completely when I turn to the right at all. 

To me, that sounds like it's the right wheel bearing starting to go out.  But ignorance is bliss and I am a very happy man.

I bought a new bearing and went to install last night.  With the trucklet up on the lift, there's no play in any of the wheels.  I spun the tires to see what I could hear, but it all sounded the same over the noise of the pads on the rotor.  I took the caliper off the right side, put the wheel back on, and it sounded like there was was some noise.  Great.  Should be it, right?

When I was spinning the right wheel, the left one would start to spin in the opposite direction as you'd expect but not as fast and would eventually stop before making a full rotation.  Spinning the left wheel gets the right one spinning along at the same speed.  At this point it was about 0100 and I hadn't really eaten anything all day and all I can think is that there's something expensive in the diff that's gone bad.

Would a failing differential make a growling noise that disappeared when turning one direction?  Are the pads against the rotor enough to give me the one-wheel-peel when I turn the other side?  That kind of noise can't really be anything but a wheel bearing, right?

I kind of think that before I took the caliper off I noticed that when I spun one side the other stayed still, but I don't know if that was real or imagined.

I would say wheel bearing. 

And that's pretty normal behavior for a diff if the transfer case defaults to disengaged. The shaft with the least resistance is going to spin and that's probably going to be the input shaft unless you have pushed the calipers back or removed one, and then the wheel may turn instead. 

Brake drag was keeping the left front spinning the same way the right side, the one with the brakes off, was spinning.

It's not necessarily the right front wheel bearing that is bad, it COULD be the left, depending on how the bearing failed.  About one in ten get quieter when you load them because you are unloading the specific race that is coming apart.

Like the bearing in teh Volvo that is now screaming louder than the engine and wind noise.  It sucks to do bearings on them because you have to take the ball joint apart to get the axles out, which requires an air hammer, and I don't like taking the calipers off because the paint chips extremely easily.  I think I got 30,000mi out of this one though!

I appreciate the sanity check. 

Looking at the right side first was based on the change in the noise with steering input, but I was trying to be a little more sure before I started throwing parts into the press.  I guess if the problem is that the noise goes away when weight transfer partially unloads the corner, I'm going to have a really hard time hearing a difference when it's dangling.  But by the same token if the noise was going away when it gets loaded just right, I should be hearing nasty noises from the left side when it's in the air.  So probably pointing to the right side.

Once that's all taken care of, though, I should probably see about making sure the calipers are all lubed up right and send the rotors out for resurfacing.  It's a really uneven amount of drag and I've had some pulsing in the pedal for a while.  The pads have at least 45k miles on them, though, and unless they were an inch thick when they were new they don't appear to be very worn.

Yep.  Can confirm: I'm just an idiot.  New wheel bearing cleaned up the noise and all is nominal.