The cabin air sensor monitors the temperature of the passenger compartment and feeds that information back to the Automatic Climate Control system to maintain the interior temperature at the desired setting.  The sensor uses a tiny fan to pull air over the actual sensing element, and that fan gets noisy if it accumulates too much dust or debris.  It's easy to pry the cover off the unit.  That exposes the sensing diode, but not the fan - it's deeper, beyond an air tube - but you should be able to spray something in the tube to clean the fan blades.  Try something like 409 cleaner.