Obviously, it's not good etiquette to be loud or talk while someone is shooting. I've had it happen a time or two, but I just concentrate on shooting and move on. Most often, it's just a competitor that's not very serious about the match, or they are nervous. I have noticed it intentionally before, but that's where preparation comes into play. If you are comfortable enough with your shooting abilities, then it's not that difficult to block them out and take good shots. You have to be able to put yourself into a focused place where outside distractions will not affect your performance.
Now if it were un-sportsman like conduct where someone was heckling you or such, then that would be time for the MD to have a talk with them. However, just simple talk during a match, should be handled pretty easily between the competitors.