Over years of instructing many people to shoot the bow, I have encountered a number of people who had string slap on their lower bow arms, but never one who had string slap on his upper bow arm. Shooting my own bow last night, I tried to imagine how it would even be possible, and couldn't come up with anything. I don't think any of the usual remedies would apply, other than Jim's suggestion to shoot with a more open stance. Perhaps you could send us a video so we can see better what's going on?