Well, first of all, I'm guessing that the servo is fighting at full travel, or trying to go farther then it should, so see if you can stop it's buzzing by adjusting the endpoint fro the ailerons to stop it from overextending. Aside from that, if that will not solve the problem it could be the servo wire, but is more likely the servo is causeing it. I would recommend getting some debonder and taking the servo out and trying a different one.