First, the ticking sound is normal. Does it click like every 12sec or so?
As for the musty odor from you AC...take the carbon filters off, let your fan run on high with outside air drawn in. Use a spray can of disinfectant like Lysol, and spray/mist into the air intake ports. Make sure you get enough in those air vents to kill all the mildew and bacteria. You might want to drape your front and rear seats with an old bedsheet just in case the disinfectant gets too wet and spatters onto the leather.
This should take care of the odor for several months, it might even last till next summer.
2012 Porsche 911 GTS
2008 ford F150 Foose Edition