Ion acoustic waves, similar to those detected by the Helios spacecraft from 0.3 to 1.0 AU, have now been detected by the Voyager spacecraft in the solar wind out to heliocentric radial distances of 1.7 AU. High bit rate waveform measurements provide the first high resolution, frequency-time spectrograms of these waves. The Voyager spectrograms show that the ion acoustic waves consist of narrowband bursts which last for a few seconds or less. The center frequency of the bursts can fluctuate rapidly in frequency, usually in the range between the electron and ion plasma frequency fp- and fp+ (These waves have been previously referred to as fp+<f<fp- noise.) Comparisons of the high-resolution spectrograms from the Voyager spacecraft with similar measurements from earth-orbiting spacecraft show that spectra of the ion acoustic waves in the solar wind at 1.7 AU are identical to spectra of short wavelength ion-acoustic waves detected upstream of the earth's magnetosphere. The latter waves have been associated with protons streaming into the solar wind from the bow shock. This close similarity suggests that the ion acoustic waves detected in the solar wind by Helios and Voyager may be driven by an ion beam instability, as has recently been suggested in a theoretical analysis by Gary.