This has gotten worse over time, I drive mostly in 2wheel Hi, gradually, a loud humming starts like that sound you hear from hugh snow tires on the pavement rolling by from a big 4x4 next to you, it's as my dash control button trying to dis-engage, i stop and hold in the 2Hi, then it goes away, but comes back, sometimes Quick, or hours later. anybody know the fix? p.s. I had the rear axle gear hub looked at, was told it's fine, changed the gear oil also.