I have an advent 7211 laptop running on Vista and my speakers have a crackly sound. However when I use headphones or external speakers there is no problem.Any ideas how to fix it?

Try updating the driver for your audio setup. A good tool for this is Drivermax from innovative solutions.

If this fails, you can go to the sound options in control panel and press the 'set to default' button unless you know what to do.

If this fails, take your computer to a technician unless you know how to remove the soundcard and speakers, reseat them, or replace them (unadvisable unless you know what you are doing).