There is a kinda rubber smell and sometimes smoke when the car is driven, what could be the problem?

It can be smelt from both the inside and outside, but more on the passenger side. It's smells when it's driven kinda hard, lots of breaking. A friend checked the car and said it could be a fan for the heater/air con. could that be it? What else could it be and how might I do some tests to rule out possibilities.