I believe the alarm is standard on all MerCruiser (and probably Volvo/OMC) engines, and is not specific to Mariah. When you turn the key, it runs a test tone, then comes on during many failures such as low/high oil pressure, low lower unit lube (I know from experience as well), high temperature, etc.

My dad's 1989 Sea Ray had it, and his 2005 Sea Ray does too. A buddy's 2006 Crownline does the exact same thing.

It may be annoying, but I'd rather put up with it than not have it! It's just a safety feature. As others have noted, start the engine right away and you'll only hear it for a split second.