A turning gear appears when I run this workflow, why?
Try:

on run {input, parameters}
    set myPassword to "My Password"

    ignoring application responses
        do shell script "sudo killall coreaudiod" password myPassword with administrator privileges
    end ignoring
end run


OR

on run {input, parameters}
    set myPassword to "My Password"

    ignoring application responses
        do shell script "sudo killall coreaudiod &amp;&gt;/dev/null &amp;" password myPassword with administrator privileges
    end ignoring
end run