An intermittant thumping has developed under the dash.
The thumping is usually corrected when the air recirculation button is activated. The thumping usually resumes sometime after the air recirculation button is deactivated. It's been occuring for six weeks. Vehicle has 41,000 miles. No lights or codes come on during the thumping. The thumping seems to be coming from behind the heater/AC controls.