Sound Problems

When i play some files, I get the picture, but i get this static noise for the sound. Most of the files that I play are fine, i checked the properties of these files and for Audio Format, it read MPEG Layer 3. I checked the properties of the files that do not work and it says nothing for Audio Format, so I think this is the problem. Since I don't even know what Audio Format is, I don't know how to fix this problem, so I could use some help. Thanks.