New to this forum. This has only happened twice now but I don't want it to get worse. I have a 4wd '98 XLT Automatic with the 4.0L SOHC, roughly 70K miles on it. Twice now i have put it into reverse but it wont engage. All i get is a very loud buzzing noise. If i put it into Drive or Park and back to Reverse it will work just fine. This has happened after its fully warmed up and when it was cold. NEW!>>> It has now made the same noise while coasting on the highway in Drive. I took my foot of the gas coming down a hill and another time when i was approaching an exit and the buzzing started. I touch the gas and it went away...let off and it started again. Checked the fluid transmission fluid and that is fine. The noise almost sounds like an electric motor. Any ideas? Another possibly unrelated matter is I get a consistant clunking when i accelerate more than like half half throttle...thinking that might have to do with the u joints but I'm throwing it in here in case it is relevant.