[mr_chin]

Just started recently. Whenever I turn on or off my monitor, this audio of like, two people with swords fighting, plays, and ends with a lion's roar...

It seems to be coming from firefox cause if it's closed, it doesn't play. When I reopen it, it comes back.

[Presto]

Does the same sound happen if you plug in a usb device, like a flash key?

It seems like it could be the sound effect that happens when a device is plugged in, and unplugged.

[underscore]

Open Firefox, then open the windows sound mixer (volume icon -> mixer) and mute Firefox, then turn off your monitor and see what happens.

[mr_chin]

Open Firefox, then open the windows sound mixer (volume icon -> mixer) and mute Firefox, then turn off your monitor and see what happens.

Okay, now it's getting creepy. The bar indicates that there is audio coming from firefox constantly, but can't hear anything through the speakers. The bar is just going up and down.

I muted firefox and turn off my monitor, no audio.

[underscore]

That's weird, check your Firefox addons for anything odd? Worst case I'd just back up your bookmarks, uninstall and reinstall.