Hmm, I've not played with sound before but can't get AVI work with any of the codecs I've got. Quicktime is fine. The only solution I can think of is for you to get Quicktime Pro. This will allow you to export the quicktime movie as an avi. Carrara allows you to scrub a sound by dragging the cursor that is at the beginning of each sound in the sequencer, but there's no playback during animation preview.