I wondered when diet would get into the discussion.  Actually, I'm a bit
surprised at the stink, Eduardo.  I've collected astraeas and tegulas both
in Florida and on the west coast and I don't recall any special problem.  I
do know that rabbits stink worse than squirrels or deer when gutting and
cleaning them and they're all vegetarians (and vertebrates).  I'd look to 
diet first anyway but that can't account for all of it since our tops don't
seem that bad.