im having diff/axle/transfer case problems too - i get from time to time a weird noise coming from what sems like the front end but when you get underneath and someone else drives it you can hear something from the back grinding like a pencil sharpener - in 2wd it only happens when i turn but i know its not the power steeting because if i sit still i can turn the swheels with no problem or noise - while this noise is happening i dont get the drop that happens after i let off the brake on a hard stop, but the noise is more frustrating than the drop - my 4wd works but sounds like something is eating metal underneath the car -i have no warning lights and tod is working but i think the tod system could be the problem - i wouldnt say i have a vibration like you say, but im curious if both our problems are related