Why do I smeel a faint burning rubber smell coming through my vents when driving?

I just came back from a 22 minute drive (I timed it), I didn't smell it in the cabin (I actually did have the heat on 3/4 because of it being a cold morning), but smelled it slightly under the hood. It was hard to tell exactly where it was coming from because the wind is dispersing it to quickly, but it seemed to favor around the coolant tank......I just waited about 5-10 minutes, and lifted the hood again. This time I don't smell it. Other things I have read also suggested a heater core issue/coolant issue, but those blogs pertained to different vehicles. I by no means know a lot about cars, that's why I am asking this as well.....what do you think