Just today I noticed a loud hum from the furnace when it's heating... my brother thinks it might be a bearing out in the blower... it still is heating but much noisier than normal

Is very posible your brother is right, it might pay to have it checked out before it goes completely out. They seem to go out on a cold dark Saturday night,when you can`t get hold of anyone to help, usually 2 or 3 am.