Noises from the Rear End

Hi All, I'm driving a 2000 Yukon Xl 2500 and recently I've been getting a buzzing vibration, too fast for wheel noise, sounds unfortunately like U Joints. It occures at about 60 MPH at part throttle and comes and goes. Taking my foot off the gas or applying the breaks makes it stop as suddenly as it starts. It sounds like I'm running on the little cuts they put on the sholders of some highways to warn you your drifting off the road.
Has anyone experienced anything like this? I've had bad U Joints but never ones that came and went and only at certain speeds.
Thanks
94

My problem was the rear end.

Has anyone experienced anything like this? I've had bad U Joints but never ones that came and went and only at certain speeds.
Thanks
94

I had the same experience in my Yukon, I thought the same as you about the vibration at variable speeds. Turned out it was the U-Joints, your situation sounds the same.