99 sonoma front end has a hum........automatic 4x4..could the hubs be locked or are they in need of some kind of lubrication...this ..of course is in 2 wheel drive...how do the auto hubs lock and unlock? thanks..ken

99 sonoma front end has a hum........automatic 4x4..could the hubs be locked or are they in need of some kind of lubrication...this ..of course is in 2 wheel drive...how do the auto hubs lock and unlock? thanks..ken

Gm does not have auto hubs.
Just Ford.
Gm uses a front axle actuator to lock in front axles.

If it has the automatic 4WD then the front driveshaft is always engaged and could be vibrating due to worn u-joints. If the 4WD was indeed locked in the truck would bind up and do funky things when cornering on dry pavement. I'd blame the front driveshaft myself. My truck has an extremely minor vibration/hum when I get over 60mph that I feel is of no issue.

Do you have push button 4WD and if so does it have 3 or 4 buttons? The 4 button style is the "automatic" version and would be like I described.