Does it appear to be a function of what interface you are using and what resolution when using that interface. For example if you are using 720p over HDMI and have your Picture Size set to PC wide do the dots appear but they don' t appear if using 1080i and Picture Size is set to TV Wide?
Or it does or does not occur when using the internal tuner.
From what distance can you see the dots and what is your normal viewing distance to the set?
Since you have had the problem on two sets I suggest that you contact Samsung Service and explain the problem to them with full details on what interfaces it occurs on, and at what distaces etc.