If you're trying the new developer preview version of OSX (10.7 - Lion) and find that the default sound output (headphones) is misbehaving, there is a quick fix for it.

According to OSX developers, if you go into the Audio MIDI Setup (under /Applications/Utilities) and change the output format from 2ch-16bit to 2ch-32bit (like in the image), that should take care of the problem.

Peace.