Many times it's an exhaust leak. Use a broom stick to touch and listen all over and see if you can find the location. Exhaust leaks do increase with rev. The air pressure can make that noise. Hope it's that. Stick will pick up vibration noise and transmit from end of stick to other end near your ear. If you are a rich guy, buy a stethoscope. Stick not great at picking up exhaust noise, but good for process of elimination. Just be aware of manifold leaks. Tighten all exhaust bolts to see if it changes. Be sure to check the exhaust flapper also. (heat riser)

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