This is a centerboard owner's only question! Straight shoal keels need not apply. My 1979 O'Day 22 centerboard was sailed for the first time this season recently, and I picked up a distinct vibration from below while reaching. I recently replaced the centerboard pennant line with a similarly-sized product. The old tie-off at the centerboard blade was encased in some putty that I cleared out to expose the hole in the board. After sending a new line through, I tied a stopper knot and stuffed the knot back into the hole, and did not putty over the hole in the board. When the wind picked up and the boat's speed increased, so did the vibration, which was audible as well as sensible to my feet on the deck. It was like a buzzing or humming that did not occur last year with the old pennant line. I tensioned the new pennant line a bit by bringing up the centerboard a little which reduced the vibration and buzzing somewhat, but not completely. Has anyone out there ever had this happen to you? Should I be concerned? Thanks for your input!