This has also been driving me nuts this year. Like Wizzlewolf, I'll also
whine back to them so they see how annoying it is.
One thing I did this year that has been working pretty well is I put up
a "whine-o-meter" (just a piece of paper that says "whine-o-meter" on
it). I did it sort of jokingly, sort of serious. The kids were surprised
when I put it up, but I don't even have to say anything anymore. My
students will catch each other and are noticing how annoying it is. So
now if someone whines (even if I don't notice it) there is always
someone saying "stop whining!" or "hey! I think that's whining. She/he
should go up (or get another check) on the 'whine-o-meter' ." It's
pretty funny. At first I was afraid they'd whine just to get their name
up, but so far that hasn't happened.