little problem with my capri 18. in pretty brisk wind say 12 to 15 the top portion of the leech of the jib flaps pretty violently. the sail is not lufting and is on the wind. im thinking one of two things. the mainsail (which is original and blown out) is causing this or the sunbrella that the p/o installed on the jib is the cause. any ideas? i know the information is pretty thin.