[Mashiro]

What exactly are the symptons? Does this beep happen on boot? When it happens do you have post -> it continues to boot into the OS. Does the beep happen during usage when you are already in the OS and are doing your work, browsing and etc? When did it start to happen? How does the system operate in general? Do you have issues with it?

Is it really a beep? Sometimes hard drives or speaks can emit a similar sound but it doesn't sound exactly like a beep from a mainboard speaker and is not as loud as a mainboard beep. Maybe even the mainboard beep speaker might have an issue and is producing a unnecessary sound. Like you might have experienced speakers popping when shutting down or starting a system. Something similar could be happening here that leads to the beep even if everything is fine.

Have you already done a diagnostics run when it occured? The Optiplex page has so many different beep codes and many of them say to "Run Diagnostics".