I have a room with roughly 100 of them and i need to find a way to disable the internal speaker, can't seem to find a way through the BIOS.
I only have two Optiplex's, but I physically terminated the internal speaker by opening the case and removing the wired connection to the speaker. Not the answer you're looking for with 100 units, but may be the only solution. Best of luck.
I have the same problem. Is there any reason unplugging the speaker wire would have a negative effect on the system? The speaker has a chip mounted on the back of it.