stills make sound jitter

trying to make the final draft of a dvd that includes three slidshows of stills as well as some videos... my problem is that now when i preview the slideshow timelines or whatch them on a burnt disk... each time the still changes the audio skips a little... whats most conffusing is that this problem did not happen on earlier versions of the disk... and i'm not aware that i have altered the slide shows in my more recent versions....

any help greatfully recieved - would love to see the back of this job....