Does your sail have a leech tension line in it? These allow you to flatten (easing) or curve/hook (tightening) the leech. It's a bit of a black art to get the right setting...but it is possible to minimize the flutter. You should not have it "helicoptering" audibly but some flutter is fine. Charlie Ogletree told me having it hooked slightly along the last inch or two is fine.

If you do not have a leech tension line, can you move the sheeting point forward/aft on your boat? This can change the force on the leech or foot...more aft sheeting point eases leech/tensions foot & vise versa.