My furnace comes on good at times, and then after about 10 seconds of coming on, it starts rumbling really bad, and shuts itself down. My husband thinks that there is air on the lines, so he bleeds it at the same time that it's rumbling, which seems to help, but when he's not doing it, the rumbling starts again. What do we do?

If you have not had the furnace serviced in the past year or two, I suggest doing so. Rumbling can be caused by anything as simple as a patially fouled nozzle to a broken heat exchanger. If you are not familiar with oil fired heating equipment, you are far ahead of the game to call a local service person who is.