What is the smell and does it have to be fixed?

A burning rubber smell under the hood might be just that - consider having your accessory drive belt inspected, as it is possible that a bearing in one of the accessories (alternator, power steering pump, air conditioning compressor, etc.) or in the tensioner mechanism might be failing. This sort of fault will often cause that particular accessory bearing to spin less freely than the others, and as a result the belt continues to pass over the associated pulley at the same speed as the engine. Essentially, the result is similar to a car spinning its tires on dry pavement - and a similar 'burning rubber' odor is the friction and heat of the rubberized belt.

If the odor is more like burning oil than burning rubber, the rear valve cover gasket is situated in a place that results in dripping oil, even small and unnoticable amounts, onto the exhaust manifold that is directly underneath the valve cover.

These two items might be places to start your inquiry. Best of luck to you!