99 Suburban Problem - any ideas?

Have a 99 Suburban with just under 100K miles. Getting a "clacking" noise coming from under (but not sure exactly where - I think the center)the vehicle as the wheels are rotating (I have pin-pointed this happening usually under 20 mph). It stops when the vehicle stops.
I had someone look at it. I looked at it but see nothing physically 'hung up' in there. I'm no vehicle expert by any means, but think that it has something to do with the tire rotation / drive shaft?

Any ideas? Appreciate the help.

Have a 99 Suburban with just under 100K miles. Getting a "clacking" noise coming from under (but not sure exactly where - I think the center)the vehicle as the wheels are rotating (I have pin-pointed this happening usually under 20 mph). It stops when the vehicle stops.
I had someone look at it. I looked at it but see nothing physically 'hung up' in there. I'm no vehicle expert by any means, but think that it has something to do with the tire rotation / drive shaft?

Any ideas? Appreciate the help.

Does the noise come from a wheel or tire? It helps to drive right next to a building or wall to help hear the noise.

If the noise is coming from the driveshaft, check the u-joints.

//2000CAYukon

I've done just that (drive along a jersey barrier) which convinces me more that its something with the drive shaft. I had sprayed out the wheels from every imagineable angle in hopes to dislodge something...no luck. Someone else (a mechanic) looked at the U-joints and thought they looked fine. It has him scratching his head too.