I have noticed two boards of mine that once they hit a certain speed, vibrate and then decelerate (9'+ boards). I feel the vibration and I'm not sure if it's the fin or from the bottom contours. Both boards that have done this to me have rounded bottoms and were made in the 60's. I've noticed this happening while I'm standing in the middle of the board and it's usually in a steeper section (I can almost hear it as well as feel it). I'll be going down the line, gaining speed then suddenly it hums and slows down. I'm hesitant to blame the fin since one of them has a huge, glassed on D fin while the other uses a 9.0 Fins Unlimited fin. The FU fin has been used multiple times in other boards without any vibration whatsoever. The best way I can describe the vibration is if you pushed very hard on a board and ran your finger along it to create a squeak, or vibration. Imagine that on a larger scale. I've checked the archives but not sure if I'm using the right terminology. Any help is appreciated.
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