Not Getting Audio on .avi's.

I spent a few days downloading some .avi's onto my computer only to find they they would not give me any audio. The .avi's that I've been using before still work just fine, but Quicktime also says that I need a new codec to play these files. However, the video still plays fine.

My question to you is, could this be the files themselves, and should I replace them if possible, or has this happened to you and do you now what codec could fix this issue. I already have a DivX and an Xvid codec and I'm using Quicktime on my Mac, if that makes a difference.

Jam it back in, in the dark.

Thanks very much, help much appreciated.

There's nowhere I can't reach.