Noticeable hum at road speeds

[spark3542]

I took a 1700 mile trip in my 83 300SD without incident, but the next day after I returned, I had a noticeable hum that I didn't have before.

I can't figure out whether it's coming from the front or rear.

From past experiences on other vehicles, it sounds to me like a bad wheel bearing.

The pitch of the hum increases with vehicle speed. It doesn't change at all with transmission gear, no difference whether on the throttle or off, it doesn't change with braking or steering, it doesn't change with Ebrake applied. I rotated the tires, with no change to the hum.

I pulled the front hubs and repacked the bearings...no change.

I see nothing in my manuals about R&Ring rear hubs.

I inspected the flex discs, but haven't changed them yet.

Point me in the right direction...should I be looking at flex discs, or dry Ujoint in the center section, or axle shafts (the boots look good), or rear wheel bearings, or something else I haven't thought of?

Thanks