|Sounds like the motor or belt. You can open up as much of it as you can and see if you can spot any obvious problem. Does it give any error message?|
A google search of mp620 grinding turned up quite a few hits but 'grinding' is a pretty generic complaint for printers. I did find this:
but I don't know if it's related to your problem.
It may end up being one of those deals where you either take it to a shop to get it fixed or throw it out and buy another.