I have a Roku Streaming Stick+, and a Vizo E55u-d2. There is a constant light crackling sound when I have the audio enabled while on the Roku stick as an input. I cannot hear this sound when I connect to alternative devices, or when I watch video casted straight to the TV. I have tried plugging the Roku into different HDMI ports, and tried plugging it straight into power with no change. I even had the Roku stick swapped out with no change.
The only way I have found to improve the noise is to not use my soundbar. This seems to be because the noise is a constant volume, so it is not as recognizable when coming from behind the TV as opposed to the soundbar in front of it.