heater smells like rubber burning on 2000 Nissan Sentra

when my heater comes on it starts smelling like rubber burning, then the smell stops, then it will start up again after awhile. What is causing that?

Asked by for the 2000 Nissan Sentra
Could possibly be that your blower motor is statrting to go. The wires to the motor could be burning. Does it make any noise? Does it smell if you turn the AC on?