Linear theory analysis and particle simulation studies were carried out in an attempt to further our understanding of the mechanisms generating broadband electrostatic noise and the effects of BEN on particles in the geomagnetic tail region. The plasma sheet particle population was modeled by counter-streaming ion beams as well as by warm ions and electrons. When the beam temperature, Tb, is much smaller than that of the warm plasma sheet electrons, Te, both beam-ion acoustics and ion-ion two-stream instabilities grow. The frequency of the ion acoustic instability is given by &ohgr;=¿(k(nb/ne)1/2cs -k∥U)≂¿k∥U≤&ohgr;pe where cs=(Te/mi)1/2 is the ion sound speed and U is the ion beam speed relative to the warm plasma sheet electrons. When the beam ion temperature is comparable to the temperature of the warm plasma sheet particles, electrostatic ion cyclotron instabilities become unstable, giving rise to low frequency noise at &ohgr;≲n&OHgr;i where &OHgr;i is the ion gyrofrequency. The simulation results confirm the presence of broadband electrostatic noise extending from &ohgr;=0 to &ohgr;=k ⋅ U≲&ohgr;pe, with an amplitude of E~mV/m, which is in good agreement with the satellite data. The observed wave intensity also peaks near perpendicular propagation, which is also in agreement with space observations.