Researchers use careful measurements of how the Sun's plasma rises and falls to detect up to a million different sound waves echoing through its gases.
Stanford Solar Center: Michelson Doppler Imager, MDI, one of the instruments on SOHO. Site provides images and results obtained from MDI.
How does the Sun sound?: Visit this site to find the answer.
Global Oscillation Network Group (GONG): contains the latest information the international GONG group has gathered through solar helioseismology. Follow the helioseismology link for additional background.