My furnace makes a humming noise every 10 minutes. The heat is still blowing so the furnace is still working. The sound only last for about 7 or 8 seconds. It sounds like when you turn the microwave oven on. Please tell me what the problem is.

It's humming because it doesn't know the words! :D

Seriously though, it cold be the blower motor getting weak and not starting up right away. I would check the capacitor first though.