I'm having the same problem with a set that is also 3.5 years old. I first noticed the dogs this morning. From what I've been reading online this seems to be a common problem with these. sets. Let me know if you hear anything back from Samsung.
Over the past few days the TV is developing white dots. It's only about 3.5 years old. We have already had to place the color wheel and that left us with dark spots, so not very happy about this new development.