I would check the SEL log for errors, but it may just be the normal USB device discovery which beeps each time it finds a USB device , bridge or hub.
You could try unplugging the USB mouse and keyboard and see if the beeps change.
I remember having this error, but with the S1200BTS. It was just that I had no USB devices plugged in (or monitor).
Once I plugged in a kb/ms/display, the post beep code was a regular one.
Hope it helps.