A spontaneous otoacoustic emission spectrum may contain equally spaced emission peaks. Then, two peaks, at frequencies,f1andf2,respectively, apparently generate a distortion product atfd=2 f1−f2[or2 f2−f1].For the three emission peaks of nine of such triplets (in six emission spectra), the phasesφ1(t),φ2(t)andφd(t)were computed, respectively. The phase differenceΔφ(t)=φd−(2φ1−φ2)[orΔφ=φd−(2φ2−φ1)] tends to lock at a plateau valueφlock(modulo 2π), but occasional jumps up or downn×2πto a neighboring plateau. Apparently, the emission at position2 f1−f2[or2 f2−f1] synchronizes to the cubic distortion product generated by the primariesf1andf2,but occasionally slips out of the synchronized regime. This behavior is consistent with a model consisting of a self-sustained oscillator in the presence of weak noise, driven by a periodic force.