Ok total guess: Was the flame cycling? Not exactly sure how to explain this... Also not sure about why this would be next to the AC. But anyway, my guess: maybe the furnace was cycling the flame off and on, perhaps they were hearing the igniter during the run. Was out for the first time this weekend myself and the first time I ran the furnace it ran for a long time to get everything warmed up. May this was what they were hearing. If so I'd say that it was normal and not to worry. But I worry about the next to the AC bit. That does not fit. Maybe one of the others will have a better idea. (Were you running the fridge on Propane? Did they perhaps hear that igniter? Or - what Korbe said?
