Multimedia. The very term requires that more than one medium be involved. Pretty pictures? Not multimedia. Silent movie? Not multimedia. If you're going to do multimedia, often that means that you're going to include sound with your visual content. But unless you've got your own recording studio or a big library of sounds, you may be out of luck.
Sound Jay offers a bunch of royalty-free sounds that you are free to use on your website or in your project. You can pick from mechanical sounds like cars and tools, electronic sounds like phones and appliances, human sounds like footsteps, and even some music tracks. Most are available as WAV files or as MP3 downloads.
You're free to use the sounds however you like, provided you don't just sell them or claim them as your own. And it might be nice to credit the site for any that you do use.
Sound Jay is a free online service. You should be able to get there and download their sound files using any modern web browser.