So I have been noticing the smell of coolant when I turn my heater on. The smell isn't too strong or unbearable but noticeable. After reading some other posts on possible causes I figure I'm looking at the heater core or the water pump. I performed an inspection of coolant fluid level and possible leaks both before and after driving with no issues. Didn't notice any mist on the windshield either. Is there any other way I can tell for sure? Since changing the heater core is a pretty big task I don't want to change it prematurely or spend money on parts I don't need..