I had a 7700 that was making a fair amount of rattling noises. Took it in for standard servicing, and found out that there were a few burrs on the bobbin carriage. The burrs were sanded down, and the machine was fine. If your machine is really making a lot of noise, I would stop sewing and take it in for servicing. You don't want to damage your machine even further by continuing to sew, hoping the problem will fix itself. If the needle is hitting anything other than fabric, the timing can be thrown off as well. General service in my area is $110, plus parts. Pricey, but worth it when you consider the value of your machine.