Apoorva , Did you tryu killing the enlightment sound demon [$killall -9 esd] , from what I know the debian systems have the esd and they cause this peoblem . Also could you try playing the a audio cd through the default player . If you can hear the sound , then is certainly a the esd . I had this issue with a good bit of boxes thats i installed ubuntu for home use .PLease let me know , I am curious it to know is this happens to all debian based systems .
Francis Pereira.