Sure does seem to be pulsing with the motor. Like not a bearing, but just a guess. Squirt soap on the belt, that will only prove it's the belt slipping. That noise will be real easy to find with a broom handle up to your ear as you touch all over or a hose or any of a dozen ways up to stethoscope. As crazy as is "sounds" it could be an exhaust leak because I keep hearing it pulse/puff/in-sync with motor. Not sure just guessing. Usually a squeaky belt will change pitch or stop squeaking when accelerated. But so does other causes. you didn't accelerate on video of eng.

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