I have a Trane XE 80 gas furnace. When the system first kicks on, a periodic beep begins--every couple of seconds or so. It continues after the blower kicks on. I'm not sure it's happening every time but it has been going on for some days. We just changed the filters--we bought this house a month ago and aren't familiar with this furnace. Is this a warning or just a reminder? Based on this forum, it seems beeps can mean several things. Should I call for service?