I decide to clean this, as it is obvious that they fall to paper from this place. When I close the front lid printer made self checking by driving the heads all the way to the left, at that moment I switched printer off, open the lid again and have completly different picture of belt. It does not looks very nice like in the previous post.
After some thinking what to do I hook it with my fingertip, stretch it a little bit and releise it, I did it several times - now I had specks all over the metal plate, and different strucutre of the belt.