Can you help on a strange problem?

Hi all,
Spent a long time yesterday downloading and installing various codecs including xvid and Divx ;-) amongst others to get some downloaded movies to work. Problem I now seem to have is that any WAV or MP?? files I now play are coming out slightly echoy and high pitched. As a result nothing sounds right. I tested a mid file and that plays OK but any mp3 or wav makes vocals sound like their on helium!!

Can you help???

Many thanks in advance folks... :D