I have had this problem with my Dyson 10. I believe that fine gritty dirt particles get in the grooves. I take a paper towel with a small bit of moisture-very small- and run it over the tracks. That seems to help. I am old and I don’t have the strength that I used to so this is an issue with this design. I am going to try to give both cleaner heads a better cleaning. The soft head seems to get quite dirty.