Would the DVD's be pirated by any chance, because if they are, then they can be quieter. If they are retail versions bought online or from a store, it shouldn't be like that. If they're pirated, there's nothing you can do, but if they've been bought, its either a problem with the disk (check it in a DVD player), and if that works, check the sound drivers for the laptop are installed correctly and that they are activated. Check any external volume controls are turned up, and that everything else is to the maximum, or loud enough to hear.