When sound waves are generated in a homogeneous rod many wavelengths in diameter by a transducer of smaller diameter affixed coaxially to its end, the pressure received by the same transducer in a pulse‐echo mode or by a similar transducer on the other end of the rod is not a monotonic function of the length of the rod. There are strong fluctuations in sound level with length. The fluctuations are caused by waveguide effects. These effects have been made inoperative in the past by techniques such as cutting screw threads on the surface of the rod. In this experiment the material of the rod itself was made inhomogeneous in a radially symmetric manner by heat treatment. It was found that the waveguide fluctuations were extinguished and the wave died out exponentially in the inhomogeneous rods. Much background noise, however, was generated through the spatial diffusion of the wave.