What is the sail doing?
Bob, What is the sail doing while the forestay is pumping? Do the tell tales look good? Where are your jib cars set? Is that 16-19 true or apparent? If it's 16-19 true and you're extremely close hauled you need to have your jib cars as far aft as possible. Check to make sure your halyard hasn't slipped as well. You need to have a very flat sail in that kind of wind on the 376. If your jib cars are center or forward and/or your halyard is loose the leach will curl and start a cycle of catching and dumping wind which will not only vibrate the jib and forestay but the mast will sometimes pump too. Give that a try and let me know how it works out.
