Crackling sound and error message

Hi,
When I play an AVI file from CD, I see it just fine, but there's a noise which does not allow me to here the voice, and none of the changes in settings eliminates it. Moreover, when I try to run an AVI file from disk, I get an error message saying: "unknown file format".
Can anyone help me solve this problem?
Thanks!

[gab]

Are you sure the .avi is ok ?
If yes, what sound do you have ? AC3 ? Mp3 ?
If AC3 check AC3 config