I just returned from a two week vacation and had an incident that I haven't seen before in the 5 years we've owned the car. Last Thursday we were driving the rim of Crater Lake, Oregon and all of a sudden a loud fan sound started coming from the rear that I deduced was the battery vent fan. I immediately checked the battery charge and it had 4 blue bars. After several minutes, the fan quit. About 2 hours later as we were leaving, actually "gliding" down the road, the fan started again; the charge indicator was 2 bars short of a maximum charge having about 8 green bars. This was after the car had been parked for 60 - 90 minutes while we had lunch. Again after several minutes the fan stopped and hasn't reoccurred. Both times the outside temperature was about 48 degrees Fahrenheit/9 Celsius. Should I take the car in to the dealer and have it checked? Does this mean I need a new battery? I had the 60,000 mile service done July 24th just before we left on vacation, but we put about 2,000 miles on during the trip.