2012 150hp Mercury Optimax 2 stroke. Serial number 1B934227. The issue... we have a intermittent issue with the engine producing a constant beep and going into guardian mode around 2K rpm. I've been on the phone with mercury support multiple times and the boat is currently at the shop... but no resolution yet. The only ecu code is overspeed. I do understand what overspeed usually feels like (such as when engine trimmed too high etc), but this really does not seem to be the problem. And the problem does not occur every trip out. I can run 5K rpm without issue and speed up / slow down and everything runs fine. But it seems as though once the problem is triggered, it is constant for a few hours during which I cannot get above 2K without beep/guardian. The stream is steady and cool, so I do not think any issue with overheating. We considered that possibly the engine was mounted too high (which it does seem high) and possibly the prop cavitating, but the prior owner states that the engine has never been moved and the current prop is 3 years old. Of course the prior owner states that this was never an issue. Only things that I have done since purchase: replaced the fuel filter, replaced lower unit oil. The gas was likely old and was 3/4 full when I purchased. I put in 10 gallons of new fuel and added a can of sea foam. Another old thread with a similar issue mentioned a "trigger module" as a culprit or throttle position sensor issue. Any ideas? Thanks.