Noisy heater/dashboard

When I slide my temperature slidebar to the far left or right the area around the dashboard or behind the it makes a clicking sound. If I move the bar a litle it will stop How can I rid the sound?

The noise might be coming from the blend door actuator.

These have a plastic coupler that engages the metal rod for the blend door. If the plastic coupler wears it can cause the blend door shaft to click as the actuator tries to control the temperature from the blend door.

Tester

I just bought an 87 Jaguar XJS coupe with only 60 k miles. The car is in perfect condition except when I turn the heat on. Cold air comes out the vent by the feet and hot air comes out the defrost vents. I could hear the levers clicking trying to open the bottom ducts. I opened the panel and found the place where it was clicking and wiggled it around. Now there is no clicking but I still have cold air coming out the bottom and hot air on top.

Can I fix this without taking the whole heating assembly out?