I had a blue star flashing and a thumping sound. I have the 770 model, so I went to the Roomba site and found this video: https://homesupport.irobot.com/app/answers/detail/a_id/2079/related/1
It was simply a matter of cleaning the front wheel (I did not know it came out to clean it) and cleaning the brush and roller (I actually replaced them since I had spare parts on hand).