If your machine has a test button that allows you to hold it in and trigger a burn while the head is not moving, then place a piece of thick card or MDF about 6 inches below the nozzle. Hold the test button for at least 5 seconds. You should end up burning a largish hole through the material but, if the small dots were caused by any form of optical scatter, then these spots would also be visible. This is a way of differentiating between spots caused by optics and spots caused by random or badly times firing. Hope that it is optics because that is generally easier to fix than random firing. my previous issues with random firing were caused by static build up. My newer generation controller boards do seam to be more immune.
Regards,