My 14 had intermittent alarm sound on my Co Gaurdian early on (20 hrs. or so ). No heat on and I would open the air vent or turn on the heat to supply more air in the cabin and the alarm would go out. I looked for the cause but before finding it, problem went away. If I recall it usually occurred on decent . I tried plugging off the water drain holes in the bottom of the fuselage (temporary tape) , I sealed the rear bulkhead thinking fumes might be back drafting, no change. I looked for firewall leakage, nothing found and no sealant added. Then it stopped. I thought it might be my monitor but somehow I drained my battery and did not know it, then tried to start the engine. My Co unit would not work after that. A new one was installed and it has not sounded off either, so it should not be the unit. I have no idea what it was, unless it was a defect with the first unit and that had something for it going bust and not trying to start the engine with a low battery. Prop never made a turn and I gave up and put a charger on it. CO unit never worked after, power spike?