The estimated densities of local field-aligned currents related to nighttime substorm onset or magnetic impulse events at cusp latitudes may exceed the threshold for the excitation of high-frequency turbulence in the topside ionosphere. The evolution of an ion-acoustic instability is shown to lead to quasi-oscillations around the saturation level. Consequent variations in anomalous conductivity will result in pulsed electron precipitation and noise generation in the Pi1 band. This proposed mechanism gives a natural interpretation to the experimentally observed coupling between localized magnetic disturbances, electron precipitation/acceleration, and bursts of high-frequency ULF noise. The alternative interpretations based on mechanisms of ion cyclotron instability stimulation and ionospheric Alfven resonator excitation can be applied only under specific plasma conditions. ¿ 1999 American Geophysical Union