NC'ing regular because this is quite mortifying.
To cut a lot of waffle out: when I jog or run, quite often I can hear my flabby belly overhang slapping against itself (last week I swear my uber-fit class partner heard it too! 
). I usually just wear normal briefs under my lycra bottoms (which clearly aren't tight enough to stop the massive jiggle).
It seems to be down to how my underwear is sitting on any given day but I can't work out whether best to be over or under the fat bit or what - I don't know till it does or doesn't happen. And I can't really go rummaging round my crotch mid class!
Was wondering if control big control pants might be an idea? Not the super heavy duty spanx, just light control?
It's a long enough road ahead without this sort of embarrassment as well 