Don't know if it will be it but, have you checked your smoke detector. Maybe the battery backup is rundown -- will beep to warn you of that fact. Just a thought.
May be way off here but do you have an electronic awning with wind sensor? If so the sensor may be blocked and the sound is coming from the black box. If so turn sensor switch off or remove blockage.
This happened to me last winter when I left the switch on and had snow on the roof.
In ours it is always the o2 alarm in the bedroom. Usually low battery. Could be fume build up from being closed up up.(new carpet, furnature, or if yoy just cleaned the carpet)
Our A&E WeatherPro automatic awning controller will beep if the wind sensor is turned on and the temperature is 30degF or below. It took me a while to track down where the beeping was coming from.
It's connected to the chassis battery so it's a good thing you noticed it when you did otherwise you may have eventually drained it to where it wouldn't start the mh