You guys with mid 100 to 150 opti’s – I have a 135 (early 2000’s motor / low hours)….haven’t used it all that much myself since purchasing a few years ago. Seems to have a mid-rpm sound like a knock, but definitely not a piston knock or real loud. Merc tech I talked with that’s worked on it mentioned it’s just the airbox sound I hear. Normal with how much vacuum these motors create. Similar to all your experiences? TIA.