burnt heat

to start 03 cavi for about a month i could hear a faint tickng /clickng coming from possibly passenger side vent when heat is on. everything worked fine each setting and all till bout a week ago i could smell almost like a burnt smell kinda hard to describe kinda like a smell from doin hard braking. the smell only comes when heat is on and today the heat was still warm but wasnt blowing as hot as it usually does. like i said everything still works sept for the smell and not getting very hot. do u think its just the resistor or maybe the cores goin out? any help? oh yea dont really smell it in the car mostly just outside