Don't things like that just drive you nuts? If you have seen two specialists, though, and had tests done it really is most likely just benign. It's hard sometimes to accept that something so irritating/uncomfortable/constant isn't harmful. I think twitching is more common in fibromites, maybe because we seem to have more muscle tension and tightness.
Funny story - well it wasn't funny at the time. When my dd was younger, she told us that it felt like her heart was "fluttering." After a visit to the pediatrician and a cardiologist and multiple tests, nothing was found. It still kept happening though, so I would tell her to let me know when she felt it. I would feel her pulse, but it wouldn't change. Finally, she pointed out where on her chest she felt the fluttering. I put my hand there, and it was a muscle twitch.
She apparently has a muscle high up in her abdomen near her ribs (left side of course, lol) that twitches. It will go in cycles and once triggered will twitch off and on for days. It seems to twitch more when she is stressed or has been exerting herself. It seems so crazy that we thought it was her heart, but I guess that is what it felt like. Twitching is often just that - twitching.
I hope you feel better soon. I know it is annoying!