I had this problem. Mine turned out to be a little white plastic gear that cracked and moved out of position. I fixed it by partially disassembling the printer (mostly the outer covers) so I could access the space where the gear was located. I used a slim piece of wood to position the gear back into correct position and then used super glue to repair it. So far it has worked.
The printer cabinet is difficult to get apart. You need to remove almost every screw you can find (#10 torx driver) and carefully unsnap the pieces. Be careful not to tug on the two ribbon cables that lead into the top of the printer. If you ruin these cables you create another problem. I broke them. I know. If you are not mechanically inclined you might as well throw it out. Cost to repair won't be cheap. HP no longer supports the printer with parts or info. Good luck!