Clicking Noise under Passenger Side Dash

[97Explorer5.0]

I have a 1997 Exploreer EB 5.0 with 85K miles. Yesterday I started hearing a variable clicking noise/thud just under the passenger glove box. I thought it was something shifting around in the glove box, but I continued to hear the clicking even at a stop. It sounds like it is the mechanism that diverts the air from the floor to the upper vents is in constant motion, thus causing the thud or click (you know the sound you hear when you divert air to the floor). It also exists when the engine is not started and the key is in the ACC position. What could it be? Your expertise in troubleshooting this weird sound is appreciated.

Regards,
Jeff

 

[Crankcase]

Sounds like your blend door is gone...run a search for "Blend door fix"