I think I would use Lens cleaner on a Q-tip. For stubborn cleaning, I might use Mothers metal polish on Q-tip followed by 99% algohol If cleaning does not work, I would look for mechanical looseness as the problem.
I have always been told to keep the Q-tips even further from the internal workings of any camera than I keep my pencil erasers. And even the gentlest variety of Mother's contains abrasives, in this case microgrit. I won't even use my wife's "Sunshine" jewelry polishing cloths on interior areas.
Better safe than sorry.