2003 Chevy Suburban leaking inside vehicle

It seems that my a/c is leaking into the floorboard on the passenger side. the local mechanic says he took a stick of some sort and cleaned out drain but it is leaking alot. The a/c also sometimes seems to make a "clicking" sound every 2-3 seconds but it's not everytime it's on. What can I do about this leaking, i'm worried that the floor will rust and rot away not to mention the smell of mildew that will start soon.