Had the same issue a few weeks ago. Replaced coupler. Replaced both belts (needed replacing)-New noise. Ordered a new idle tensioner because I located the sound directly.
At this point.had been scratching my head for a weeks trying to figure out what the deal was. Had the SC ported, plugged and severely cleaned recently so it had all new fluids and is in great shape.

Turns out my belt was one rib off -_- son of a b*itch.

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