Monocogger

I need a little help on tracking down a new issue on my 97 jeep cherokee. After sitting in the garage for a week I pulled it out and started to drive down the street. Every time I came to a stop or made a left hand turn it sounded like somebody was dumping a handfull of grit into the blower motor. I could hear it all bouncing around in the dash and flinging off of the fan blades. After that, smoke started pouring out of the heater vents. Besides the sound of the grit in the fan nothing else sounded or acted strange. The smoke started off smelling like burnt cookies, then burnt paper, then cigarette smoke, then burnt marshmallows and finally burnt tar. It doesn't smell electrical so I don't think the fan motor is causing the problem. I asked my friend about it and he thinks that I have an air cooled fan speed resistor and that the grit that is bouncing around in my vents is landing on the hot resistor and burning. Do you guys have any thoughts? The heater core can't get hot enough to cause smoke. Bad smells, yes. But actual smoke, no.