In the inspection of titanium material intended for use in aircraft engines, a number of unusual phenomena are observed, including significant fluctuations of the amplitude and phase of back-surface echoes and of the amplitudes of pulse-echo signals from nominally identical flaws[1]. Practical implications include a broadening of the probability of detection curves and difficulties in determining the ultrasonic attenuation, a parameter used in interpreting flaw response data. Incorrect determination of attenuation can lead to errors in distance-gain corrections and hence in estimates of the magnitude of the flaw response. In this paper, we report experiments designed to elucidate the mechanisms responsible for these signal fluctuations.