Audio Problem

I am trying to figure out why the audio in some movies that I have copied will raise and lower. At first I thought maybe it was due to compression but a moive that had no compression did the same thing yesterday. I have tried Recode, CloneDVD2, DVD Shrink and DVD Rebuilder Pro and the same thing happens. Has anyone else ever had this happen or can anyone offer a suggestion?

Thanks

You’ve the same with your originals?