Piezo Alarm Question

[Umma Gumma]

I have a 2004 115 Optimax. The piezo alarm under the dash is shot (no beep when turning key to "on"), so I went to radio shack today and picked up another. When I hooked it up and turned the engine to "on", I get a loud, noticeable beep. Problem is after the first short, loud beep, I get what sounds like continuous feedback at a much lower volume. There's a distinct difference between the "beep" and the noise afterwards. I checked voltage at the piezo plugs, and it's 12v anytime the key is on.

Do I have a short somewhere, or is the aftermarket piezo not the correct one? It indicates it works between 5v and 28v or so.

Thanks for any thoughts on the issue.

[boatfixer]

What is the history? Have you owned it for sometime and it had just quit working?

I guess my first thought it that something in the warning system is sending the signal, whether its one sensors or the warning module is 10-7. Im not completely familiar with the Opti's system but constant voltage doesn't sound normal.