This could be either your drum cartridge or your fuser unit.
Take your toner cartridge out and look right up front where the drum cartridge empties 'waste toner' back into the toner cartridge. There's a little flap there that slides back and forth on the very end. Slide it back and see if toner is packed in there solid. If so, vacuum it out. Then you'll have to replace that drum. Sometimes you can salvage them by cleaning out all the waste toner, but usually the gear in back has already stripped and it's no use.
If everything looks fine with the cartridges, it's probably the fuser. You can buy a new one here:
The fuser is that part of the machine that gets real hot. If you open the right side door, it'll be right close to the top. There are usually 4 screws holding it in place. If you take those screws out, you should be able to hold it away from the machine while it's running (you'll have to cheat the door). If the grinding stops as soon as you pull the fuser away, that's probably your problem.
Let me know if any of this sounds too technical. eric AT essonline.us