Issue with sound level.

[ilikestuff]

In some of the files I'm watching the background noise is quite loud while the character's dialog is very faint; almost as if the two sound streams are reversed. I'm not sure if the term "sound stream" is correct, but that's what it seems like. I know there's an easy fix for this as I had the same problem on an old laptop. I just can't recall how to do it. Is this an AC3 Filter issue? Any suggestions?