Spectra of ultrasonic cavitation noise were obtained in liquid helium and liquid nitrogen. A subharmonic response at half the driving frequency was found to be present at all times. In the case of liquid helium, the relative intensity of this subharmonic showed a peak at the λ point. The background noise intensity was also higher in heliumII. A tendency for the half‐order subharmonic to increase with static pressure was also found both for heliumIand nitrogen. A correlation between the onset of the subharmonic audible‐frequency noise and the white‐noise background was also found. The variation of the intensity of the first overtone with increasing driving voltage was found to be different in heliumIIthan in other liquids. It is argued that many of these phenomena arise from the effect on bubble dynamics of the efficient heat transport in heliumII.