Having taken out my used 99 Powerquest Enticer 29 FX for the first time since buying it I ran into a couple of issues. While idling I heard a warning alarm going off. It was not like the alarm that goes off when you first turn on the ignition which is a loud continuous sound. The sound I was hearing while idling was more of a subdued one. It would go on for one second and then would go off for two seconds and then go back on following the same sequence. It would then shut off once I got over 20 MPH. As soon as I got off of plane and started idling it would turn itself back on. With open exhaust it was hard to isolate where the beeping was coming from but I believe it was coming from under my gauge cluster. I had no over heating, no low oil pressure or no low lube levels in either of my gear lube bottles mounted on my Mercruisers so what could be beeping? I did notice my depth sounder was only flashing zero displays so that also is not working.

What engine? That alarm is usually a sensor. Check to see a wire hasn't come one of the senders (water temp, oil, IAP, etc).

Being a 1999, the only things that will set off the alarm are:
High water temp
Low oil pressure
Low drive fluid

There are sensors on the engine are separate from the guage sensors. You could have a bad sensor or an alarm wire grouding out. The sensors all use a tan wire with a blue stripe.

The engines are Mercruiser 7.4 MPI's.

Still would like to know, if it is an alarm for any of these three warnings, would it be a steady sound or one that would go off for one second, turn off for 2 seconds and then turn back on for the same type of sequence. I would think, if it was any of the three, it would be a steady sounding alarm. Just need to get that answered.
Thanks

Depending upon intermittent high readings the alarm will sound then silence as the readings rise and fall.

Mine was just going off the other day when I started my boat after a drive oil change. It was beeping exactly like yours. The gear lube reservoir sensor was stuck down.
You can figure out what sensor is setting it off by unplugging the sensors one at a time.