I've never had that problem with youtube, but sure do (well, did) have it with soundcloud and vimeo. In my case the cause certainly was not the computer volume, nor the site/file volume, nor my firewall (gave temporary trusted site status to check the last one, as my general security level is fairly high).

A bit of related thread drift: I soon gave up on and deleted my vimeo account because their help people were useless to a degree that wasn't even entertaining. My soundcloud account may end up a "gone-er" too--there is so much more music to get on with and so little time in a day already that (until I'm cornered into HAVING to do so) I'm not willing to prioritize time to figure out user-unfriendly sites. Far easier to share audio only by turning it into a "video" with a movie editor, just add a photo to my mp3 and youtube will accept it as a movie. Most of my use of these sites is to share rehearsal recordings with the people who were rehearsing. I sure do hope that frogprince's issue is not a harbinger of me having a similar problem at youtube! In my "spare time" I may try soundclick as several people here use it and (so far!) I do get the sound for their files with no problem. Dang technology. Love it. Hate it.