After reading a few post here about driving and switching into and out of 4 WD I was out today on the road trying it out. Everything worked but when I am driving in 4WD and switch back into 2WD I start to get a rumbling sound inside my X when I get to about 45MPH and more. Anything below 45 everything feels fine. When I unlock the diff by backing up and hear the click and then start to drive, I don't get that rumbling sound. Is this normal with all of you? Thanks for any input.