Some interplanetary shocks detected by ISEE-3 are preceded by many hours of strongly-enhanced plasma wave noise at a few kHz, while others have essentially no wave precursors above background. It has been shown that these extremes correspond to quasi-parallel and quasi-perpendicular shocks, respectively, based on the instantaneous orientation angle &thgr;Bn of the interplanetary magnetic field (IMF) to the shock normal at the time the shocks cross the spacecraft. We show that precursor wave noise level is correlated with field orientation and an extrapolated &thgr;Bn throughout the preshock observation interval for two contrasting active and quiet cases, and that intermediate, variable noise levels correspond to intermediate, variable IMF orientations. We infer that foreshocks are an intrinsic part of the structure of quasi-parallel interplanetary shocks.