Tail was off the ground, so the tail wheel was not the problem. I now have the cables about as Joe suggests. No buzz, only a trace of singing. I think it may have been uneven tension on the cables from torsion. When I detached the adjusting clevis from the control horn, there was a fair amount (perhaps 8-10 turns) of twist in the cables. Problem solved now, I think. I appreciate all the advice.

Thanks all.