My 02 blazer has a humming noise with a faint vibration while in 2WD. If I switch to 4WD the noise goes away. When I switch back to 2WD the noise is silent for a few minutes then returns. It seemslike while in 2wd the 4wd in not completely disengaged and something is slightly touching causing the humming noise? Is that possible? I know there is an electric solenoid in the system for switching from2wd to 4wd but I'm not sure how the system works and what the problem could be. I had it to a dealership twice and the Chevrolet mechanic could never hear or feel anything.Ithink he's deaf. Can anyone help? Thanks

 

Welcome to the forum, The 4wd is staying engaged because of a failing vacuum switch on top of the t-case...replace it (about $30.00) and that will cure the slow disengagement problem. The noise is a different animal...being that the noise is present only in 2wd...it has to be something in the front differential that is turning in 2wd, like an axle shaft bearing.....but I would fix that vacuum switch first to see if that effects the noise...it could just be neverFULLY disengaging the front axle.