Disturbance after render (white backgound)

Hello,
I have a question regarding a weird disturbance I get, after rendering a graph (.jpg) on top of my timeline with a blank slightly off-white background.

I attached a screen shot as .png file.

I would appreciate any hints.

Thank you!
-Marco

Could somebody give me a hint what I could do?

This disturbance happens all the time in my video.

I would appreciate help!

Thank you!
-Marco