Put a scan tool on it!

Fwiw
 

Ran into this once, If you are using stock Merc feed back non-mechanical

It was a crossed connection between the drive trim limit switch and drive angle gauge sender...

It means take it to a shop and ask someone that knows what the hell they're doing. The last time mine beeped that much, one of my headers cracked and pissed water into a cylinder. Ended up replacing more than a header.

mmm... good call! won't take a chance!