i hav stx and starting to hear a humming noise on driver side at speed 50 or greater and also a rattling noise on passenger side . i changed brake pads on the front today and when i was turning passenger front wheel i hear this clicking or rattling noise. after i changed front pads , i took it for a ride and noise still there. i put it in four wheel and noise stopped and then back out and noise was there. i pullled the hose off vaccum line from solinoid and see if that would help but it did not. so my guess that my wife took my truck on trip to the beach 300 miles or so and she mentioned the noise she heard. so my gusss it is shot. do you think drive axle will be ok?.
i didn't hear the on driver side, probably paying attention to the noise on passenger side. if hum is still there you think tire or wheel bearing going bad. when turned wheel on driver side i saw the axle turning on passenger side. is this normal. the truck has 96,000 miles on it.

 

Sounds like IWE, independent wheel end, it is what engages the front hubs for 4x4. Try disconnecting power to vaccuum switch. The system has check valves to stop vaccuum bleed off, i.e. yanking a vaccume line.