回答“2011 Ford F-150 fan switch creates a knocking like noise under dash?”I've replaced the blend door actuator 3-times in my 2011 F150 and am headed to O'reilly's now to get another one! Good thing they have a lifetime warranty on the part!! I watched a couple of YouTube videos that show you how to do it. It's frustrating that it keeps breaking and has since about 2014....It IS a common problem on the F150 and other models that use the same part. The clicking sound is the broken plastic gear inside the blend door actuator (moving the knob changes the vent from cold to hot). Usually this will make the clicking sound around the last 2 "cold" positions on the control knob (the one with red and blue color indication lines around the knob). I need ALL of the cold available as I live in 115 degree summer weather in California. The Ford dealer told me that it will cost about $250 for them to do it; I do it in about 1/2 hour and the initial cost of the part was about $24.99.