I have encountered this problem with a few machines I have in the field. What I've noticed it boils down to is the charge corona cleaner. I recommend you turn off the corona cleaner, and REMOVE the wire cleaning assembly (the sponge part that actually pinches the wire). You have to leave the gear / mounting assym on the unit itself because there are home positioning sensors that will go nuts if you take them off. Just remove the actual CLEANER only. You also might have to change out the wire, that cleaner is notorious for breaking wires. If you have anymore questions about the procedure for this just let me know.
Tom