Okay, I've just gone and done some testing for you. Next/Previous chapter is pretty instantaneous, with no sound dip. I think I have found a layer change (Terminator 2 Special Edition, R2 81mins 6 seconds). The layer change is instantaneous, with no sound dip/pause, but there is as far as I can tell one skipped frame on the video that is completely repeatable (even in slo-mo) at exactly the same spot. If you blink or you're not sensitised you'll miss it, there's no sound dip cue for you to notice it. It is between dialogue, but I can't detect any dip in sound on the background noise. Like I said though, there is a momentary dip at the beginning of a title. I've even heard it when you switch menus (for instance when you go from the main menu to the sound setup on the T2 disc). I think it's buffering or seeking, and it only happens for that one half a second right at the beginning of a new title.