It can be dry ink from underneath the carriage/heads or it can be the rubber belt (that moves the carriage) flaking. It is quite common after a couple of years.
Check the belt first, open the window cover and move your hand along the belt, see if it flakes as you gently rub it. Check also for signs of wearing. If that is the problem, the only solution is a new belt.
If the belt is OK I would advise a good clean up of the carriage and heads. Search for older posts on this forum on how to do it, I remember a quite good one but don't have the link at hand.