Simultaneous observations by Wind and IMP-8 intheupstreamregiononMay11,1999,whenthesolarwind density was well below its usual values and the IMF was generally weakly northward, indicate there were upstream waves present in the foreshock, but wave power was an or- der of magnitude weaker than usual due to an extremely weak bow shock and tenuous solar wind plasma. Magnetic pulsations in the magnetosphere have been observed in the magnetic eld data from Polar and at mid-latitude ground stations. By comparing May 11 with a control day under normal solar wind conditions and with a similar foreshock geometry, we nd that the magnetosphere was much qui- eterthanusual. ThePc 3-4 waveswere nearly absentinthe dayside magnetosphere both at Polar and as seen at mid- latitude ground stations even through the foreshock geom- etry was favorable for the generation of these waves. Since the solar wind speed was not unusual on this day, these ob- servations suggest that it is the Mach number of the solar wind flow relative to the magnetosphere that controls the amplitude of Pc 3-4 waves in the magnetosphere.