Laptop beeps after resuming from suspension

[Thomas Dean <tdean9db@xxxxxxxxx>]

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