Sound Issues

I seem to be having some strange issues (Only on GW)

Whenever I enter a zone I get ALL ambient sounds played as if I was standing next to it (Waterfall) then half a second later it's gone, It only occurs when I enter an area and no where else.

Also if I ALT+TAB out and back in, Alot of the sounds such as casting spells or the sound of a sword hitting disapears.

Has anyone else had this problem and how did they fix it?