It's time for ... NAME THAT NOISE! I think it's a bearing

[ForbesZ]

I have an 01 4.4 sport with 102,000 miles on it. I noticed what sounds like a worn bearing and it seems to be most noticeable around 55 MPH when coasting but can actually be heard at most speeds between 40 and 70 MPH. I can't really tell where it is coming from (doesn't sound like it's coming from any particular corner of the vehicle) but it is definitly there and varies directly to vehicle speed, not engine RPM or what gear the transmission is in. This leads me to believe it's either a wheel bearing or something in the transfer case, differentials, or driveshafts. I don't think it's the tires since they are fairly new, the tread is absolutely flat (not feathered), and the alignment was just done. It doesn't sound like a "whirring" type tire noise either - it resonates through the vehicle more than that. It's amost like driving on very faint rumble strips.

What bearing tends to be the first to wear out on the E53s? Is there a bearing on the rear drive shaft?

Any help is appreciated!