It is not uncommon to smell oil or burn metal when you first fire a new furnace. These smells are common and are the results of manufacturing, but should come from the inside of the heat exchanger and would come out of the vents and the area around the furnace. Any smell you smell from the furnace area after initial start up is produced outside the heat exchanger if it last any length of time I would assume is an indication something is in contact with the heat exchanger shell, not a good thing. Rubber would not be a smell created by any level of manufacturing.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles