Hi,
Which kind of connection are you using for your monitor? DVI or HDMI?
I had same problem and it appears that my DVI cable was not connected properly, not sitting real tight. Hardware removed sound would appear if you are using HDMI but i think that you may have same problem with cable. Either not connected properly or mailfunctioning or even worse one of your connectiors on video card or monitor is mailfunctioning.
Try replug it, straight it up a bit or try another cable.
Best regards