2007 explorer NO HEAT AND CLICKING NOISE????

OK I DO NOT LIKE NEW CARS JUST TO MUCH ELECTRICAL IN THEM BUT BESIDES THAT MY WIFE HAS A 2007 EXPLORER 2WD 4.0 V6 AND ITS NOT BLOWING ANY HEAT REPLACED BAD THERMOSTAT BOUT A MONTH OR SO AGO COOLANT LEVEL IS SITTING AT FULL COLD WHEN I CHECKED IT COLD BLOWER WORKS SPEED WORKS BUT THERE IS A CLICKING NOISE COMING FROM BEHIND THE RADIO/ HEATER CONTROLS AND NO CHECK ENGINE LIGHT AS OF YET THINKING HEATER CORE BUT CLICKING IS MAKING ME WONDER BUT TRUTHFULLY I WOULDNT KNOW WHERE TO START WITH THIS TRUCK NEVER HAVE HAD A PROBLEM LIKE THIS BEFORE SO PLEASE HELP ME OUT PEOPLE THANKS FOR YOUR TIME