I had a similar problem in finger style. It turned out that when I "barred" 2 strings with my 3rd (ring finger), I got a clack. Only really raising the action pretty high would cure it---until I discovered it was always with a certain kind of fingering. I changed that fingering to something better.
Slow down and really examine what's going on before you make any more set-up changes. Figure out exactly WHERE the sound is coming from, when it happens, and what the common factors are.
I bet you may find it IS a technique issue. If so, don't sweat that. Once you spot it, you can easily fix it. If it is not technique, then maybe the other guys are right, it is part of the slap thang. Just be sure you have eliminated all other possibilities.
Big question: determine if you get it fingerstyle in any kind of consistent pattern of strings/fingering. That is a good clue it is left hand, not right hand....
