Strange burnt smell
 

All of the following events started within the past week. I have noticed a burnt pizza crust/ toast smell in the car after running the heat on high while I commute to work. I have not noticed any problems with the operation of the car, nor have I noticed any other burning smell. I have been in the unfortunate position of smelling the variety of smells that can come from a car with problems, but this is a first for me? Any assistance is appreciated.

When was the last time the cabin air filter was changed/checked?