Firstly, thanks lordsmurf!
That was driving me nuts and it's good to know there's nothing wrong in that regard.
Honestly, I don't have a clue why it's so noisy, usually it's a mostly clean signal, as seen on the attachment. Now I'm worried about those faint horizontal lines throughout the picture. After some research, I suspected it's chroma/luma crosstalk, however, examples show diagonal lines intead of straight horizontal lines.
But what do you think? Please, I'd really appreciate your appraisal.