Flux Transfer Events at the dayside magnetopause are considered to be a result of transient and patchy reconnection taking place at the dayside magnetopause. A mechanism is proposed for generation of low-frequency electrostatic waves often observed in the events. In the open flux tube model of Flux Transfer Events magnetosheath and magnetospheric plasma populations mix on the open field lines. Using the zero net current condition, we show that the magnetosheath electrons are accelerated in order to compensate the current carried by hot magnetosphere electrons. A number of realistic sets of parameters for both plasma populations were used for numerical solution of the dispersion relation in the electrostatic approximation. Some of the solutions are presented. Questions related to the instability are discussed.