I have a 2003 Honda Civic with ~40,000 miles on it. I have noticed a strange sound recently and can replicate it fairly repeatedly. I turn the fan on to run cold air through my windshield defroster and this runs the AC through the defroster. I then turn off the fan (after running it for only 5-10 seconds) and turn the air setting to the front vents (which would blow air at chest level). I do not turn the fan on after turning the air setting to the front vents. After waiting for about 4-5 seconds, I hear a popping-like sound that seems to come from an area just under the dashboard and roughly above the area where I control the air settings. Another way to possibly describe the sound is as if someone did a single, heavy tap on the dashboard. Does anyone have an idea for what this noise may be and why it happens? As I said, I can replicate this noise any time I want, regardless of whether the car is in motion or at a stop. Thanks for any ideas you have.
[b]What you’re probably hearing is a vent door in the system slamming shut when you switch from defrost to the dash vents. These doors usually have some sort of foam seal on them that prevents that noise. The foam on yours probably fell off.