Musicians in general noodle because they get bored. Rehearsing can be boring but the reality is that it is work and work isn't always fun. However, work is also always required if you want to improve, and a short attention span is no excuse for screwing around and wasting the other musicians' time. Ultimately, noodling stems from an unprofessional attitude and weak resolve, and it's a bad habit that is tolerable to a small degree but should never interfere with work getting done.
The drummer in the rock band I play in used to muck around a fair bit in between songs (though not during gigs, fortunately), and it was annoying me and the guitarist/singer. After that, and him once conceding that he cancelled a practice because he "couldn't be ****ed rehearsing" that evening, I faced him one night and just said "We generally plan to get through the set 3-4 times each night, which we were doing before, but we're mucking around too much in between songs and we need to focus on just bashing the set out twice before we even start thinking about doing anything else. We need to put the work in if we're going to get anywhere, so we'll just have to buck up and do it."
People generally have an aversion to conceding their weaknesses, so he didn't come out with the "I need a break" bull**** that we usually got from him, and he knew full well that when I said "we" I really meant "you", but by not actually saying that I avoided starting a conflict. In bands, there is no "I" or "you", there is only "us", and speaking to people accordingly means that you're never calling them out personally; in my experience it's the most effective way to just deal with problems and not start personal arguments.
My recommendation is to talk to the guitarists about the problems they're causing, saying "we" are "having" these problems, and talk about what you think "we" need to do to fix them so that "we" can benefit. Human beings are stupid, myopic, self-absorbed creatures, but they do respond very well to guilt, if you really hammer it in.
