Dian,
I have the 870 and have no problems like that at all. I do know the Sapphire does not like Coats & Clark thread. It sews okay with C&C but makes a terrible noise, like telling me to stop using this thread. My dealer says they changed companies that winds the thread on the spool and a lot of people are complaining. These are all the new spools of C&C. Take your sapphire back to where you bought it tho, and they should be able to help you. It should still be in warranty, as they haven't been out on the market long.