Dash noise - Climate Control Sensor?
 

I have a 03 Silverado with an odd dashboard noise. The noise is hard to describe but reminds me of a ducks quack. The noise lasts for 1 second at 1 second intervals and can be very irritating.
It seems linked to the dual electronic climate control. When I spin the thermostat dials to the highest or lowest temperature settings the noise stops - temporarily. The sound is coming from the defroster vent area on the driver side dash.
I'm thinking it may be an interior temperature sensor but who knows. I dont relish the idea of ripping into the dash.
Any ideas?