This didn't bother me until one of my website users pointed it out but it seems my embedded Windows Media Player set to play an MP3 file causes the page to be in a constant state of loading. Not that the page itself doesn't load, but it the tab has the spinny thing, and the status bar at the bottom of the browser never stops saying "loading from blah.com..." The player doesn't have autostart, but is it sort of preloading the file or something? It's getting me really annoyed and makes the site seem slow when it isn't.