Mitsubishi Galant with no heat

I have a 2003 Mitsubishi Galant, 4 cylindar, 110,000 miles.

Fall of 2006 I began using my heater as the season grew colder. One morning, I turned the knob from cold to heat. I heard a loud clicking/grinding noise coming from behind the center of the dash. The heat worked fine. This continued off and on.

Then one morning, no grinding noise from cold to heat, and no heat, just cold. This pattern continues. When I hear the loud grinding/clicking noise, I get heat. When I hear nothing, I get no heat. More often than not anymore I get no clicking and no heat. Any ideas? Thanks, Eric