I've had fluttering feelings in my guts for no reason. If you're not having any pain or bowel problems, then it may very well be some sort of mescle twitch. I sometimes get eye twitches off and on for several days. Lack of sleep and stress seem to cause mine, so if you're in a similar way right now, try sleeping more and getting away from stress (or at least counteract it with relaxation techniques).
The other thing that has caused fluttering in my bowels are sugar alcohols. These are found in sugar-free candy, gum, mints, ice cream, etc., etc. If you've been eating anything sugar-free lately (other than colas; they use Equal or Sweet-N-Low), cut that out and see if your twitches go away. They cause bowel problems in a lot of people.