I have a 2008 F-150 and just last week started experiencing an issue. When I start the truck there is a very rapid fire clicking noise that sounds like it is coming from where the CD player is located in the dash. The sounds lasts a couple of seconds and then stops. While driving the vehicle the sounds repeats about every 5-10 minutes. This is happening with the thermostat turned off. I have posted a link below to a video of me starting the truck so you can hear the sound. Any help with diagnosis would be greatly appreciated.

 

When I first read the title, I thought it would've been the blend door actuator motor, but it sounds like something else.

It sounds like the CD player has something stuck in it. Have you tried unplugging the CD player and seeing if that stops the noise?