maoning/humming noise front end 01 ranger

Does anyone have any ideas where my 2001 ranger 4wd has a humming/moaning noise is coming from? It almost sounds like the 4wd is locked. Noise does not get louder the faster i drive. The noise can dissappear sometimes when turning left. Any thoughts would be appreciated. thanks:confused:

The wheel bearings could be the problem. Jack it up and spin the wheels. Check for roughness