Driving to work this morning, decidedd to test the 4x4 on dry pavement.
pushed the 4hi button and the front end started vibrating, put it back in 2lo and slowly the noise went away. there is a slght humming from the front end constantly, even before the vibration in 4x4, i assumed that was tires and rotated them out, noise still there, just bought the truck a couple weeks ago and trying to figure out whats normal and whats not any ideas?

 

1996 blazer 4 door 4x4, 235/70/r15

 

have you had a look at the drive shaft from t-case to front diff?
maybe its the u-joints on there.