A few weeks ago a thumping noise began from behind the heat/AC control area.
41,000 miles. The thumping is intermittant. If the air recirculation button is activated, the thumping stops. When the air recirculation button is deactivated, the thumping begins again, sometimes immediately, sometimes soon after or sometimes later. No engine warning lights are on during the thumping. Heat, AC and fan all work properly.