[arch-general] Laptop beeps after resuming from suspension

Hi folks, I have an encounter with a small but annoying problem. After typing pm-suspend and then resuming my laptop, it sometimes beeps, which never happens if I haven't ever suspend it. For example, when I type too much backspace in VIM, it beeps; when I push the shutdown button, it beeps; when I type Page Down button at the end of the text, it beeps, too. Could you please tell me how to shut its beeping? Thanks, Thomas