Scrambled sound on Mac Pro ( after Quicktime Pro registration?)

The sound on my Mac has gone scrambled. It sounds like I am listening to music underwater. I was listening to music this afternoon, after I registered and upgraded Quicktime this evening I experienced this problem. It is happening for all aps, itunes, FCE.

I can only think that it's got something to do with the quicktime upgrade.

What to do?

If there is a Plonker of the Day thread in the Mods area, well you can add me to it.

I am using headphones and the plug was ever-so-slightly unplugged.