It's hard to see the issue from the images you posted. First I would clean the inside of the main drawer assy.
If its small black dots it's most likely an issue with the IBT cleaning blade. Try preforming a hard stop. After the sheet is pulled open the door causing the printer to stop. Pull the IBT Belt assy out and inspect the image on it. It the defect is present I would assume it's an IBT blade issue.