'02 F350, 4x4, manual hubs, and manual xfer case. So with the front hubs locked, xfer case in 4x4, there's a rumbling noise from the front end. Sounds like bad u-joints or bearings.

With front hubs locked, xfer case in 2wd, no rumbling noise, but there's a clicking sound on sharp turns - sounds like bad front u-joints.

With front hubs unlocked, xfer case in 4x4, no rumbling noise.

Jacked up both front wheels, no noticeable play which might indicate bad front bearings.

Front axle u-joints don't feel loose or sloppy by hand.

Any other tests I can perform that would help ID the problem?

Thanks!