Q: rythmic thumping in right rear panel on 2005 Ford Expedition

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when Exp is running there is a rythmic thumping like someone patting a drum coming from the right rear panel above the tire. Also the check engine light is on.
(1) Answer
(1) Comments
I can bet that you have rear climate control in your Expedition. The rear climate evaporator case has blend doors that route the desired air temperature and position (floor or upper panel). These blend door actuators are known to strip out the gears inside them and make a repetitive click or thump noise. There are two in the rear case and it may be worth doing both while your mechanic is in there.
Thank you, that was very helpful and has now been fixed. It was so nice to get a reply so quickly and it was like having a 2nd opinion when the dealer diagonosed the same thing. Thank you!