An apparatus includes a constant on-time or constant off-time (COT) switching regulator configured to generate an output signal. The switching regulator includes a switch that is turned on or off for a specified amount of time during each of multiple switching cycles. The apparatus also includes a modulator configured to modulate the specified amount of time that the switch is turned on or off during at least some of the switching cycles. The specified amount of time that the switch is turned on or off during each of the switching cycles could be equal to tON/OFF+ΔtMODF(ωMOD), where tON/OFF denotes a constant amount of time, ΔtMOD denotes an amplitude of the second signal, ωMOD denotes a frequency of the second signal, and F( ) denotes a modulation function. This could help to modulate switching noise over a range of frequencies and spread electro-magnetic interference generated by the switching regulator.