Hi Lisa! Sorry to hear that Chumley is plucking, What a bummer!
But glad the vet has cleared him of any medical problems being the cause. Have you ever caught Chumley in the act of plucking? Do you know approximately what time of day he is most likely to preen or take a nap? That may be the time that he is plucking. If he is doing it around the same time every day, maybe you can take him out of his cage before it starts. Provide him with some fun activities to help keep his mind occupied with other things. The important thing is to do this BEFORE the plucking starts. Of course, the only drawback to this is if you are not around during the day. Then I would rearrange the inside of his cage frequently and keep him busy with new toys. They have foraging toys you can buy. Just make sure you check the measurements. Some are too big for our little guys. You can also try putting a bowl in his cage with crumpled paper and filling it with treats and fun little toys, etc. Pugsley loves digging for buttons. People use baby cams to watch their birds when they are away from home. That might give you some insight into what Chumley is doing when you are not around. You haven't changed his food or anything else lately, have you? You know how sensitive they are! 