This took me some time to figure out and the culprit is quite unusual, hence I decided to reproduce the solution here. If you get choppy sound and a weird beat of beeps when you play (low sound quality) flash videos under 64-bit Linux, then it is because of a change in memcpy provided by glibc. Linux Torwalds suggested the following fix which works for me:
Silke’s Most Recent Project
Silke worked on this for a couple of weeks (with overtime and all that) and it is finally done. Figured, I should spread the word.