In this note we report on the recent analysis of occurrences and properties of kHz QPOs in the source 4U 1636-53. We find a prominent frequency (or a narrow frequency region) that separates upper and lower QPO observations. The two QPO modes are then simultaneously detected mainly in the vicinity of this transition points. We show that this can be understood in terms of correlations of QPO properties with frequency, such as quality factor and rms amplitude. We find that rms amplitudes and quality factors of both QPOs nearly equal at the transition point. In addition, the QPO frequencies are nearly commensurable there.