This paper considers the generation of enhanced ion acoustic fluctuations by field-aligned ion beams upstream from the earth's bow shock. Steep slopes in the beam distribution parallel and possibly strongly oblique to the magnetic field are correlated with bursts of ion acoustic noise in the upstream region. Linear theory shows that it is the slope of the beam distribution at oblique angles to the magnetic field that determines the growth rate of the ion/ion acoustic instabilty. Because of instrument limitations we suggest but cannot confirm that enhanced ion acoustic fluctuations in the upstream region and in the presence of field-aligned beams are driven by such steep-sided distributions. ¿American Geophysical Union 1987