This paper presents a new approach to rejection of sinusoidal disturbances acting at the output of a discrete-time complexvalued linear stable plant (e.g. acoustic channel) with unknown and possibly time-varying dynamics. It is assumed that the instantaneous frequency of the sinusoidal disturbance may be slowly varying with time and that the output signal is contaminated with wideband measurement noise. It is not assumed that a reference signal, correlated with the disturbance, is available. The proposed disturbance rejection algorithm automatically adjusts its adaptation gains to the rate of system and/or disturbance variation.