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.
http://www.noao.edu/education/ighelio/solar_music.html
http://soi.stanford.edu/results/
Stanford Solar Center: Michelson Doppler Imager, MDI, one of the
instruments on SOHO. Site provides images and results obtained from MDI.
http://soi.stanford.edu/results/sounds.html
How does the Sun sound?: Visit this site to find the answer.
http://helios.tuc.noao.edu/
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.