Seeing as I don't know next to anything about heating/ac, I decided I'd post here to see if anyone had any idea.

The setup is some old heat pump/furnace/water heater/etc, which all of a sudden at around 3:00am this morning decided to make a VERY loud noise. I had to shut it off (the furnace is a gas furnace, if that helps) using a switch that was installed for that very purpose, as the unit is rather old but generally still works.

Basically, the motor makes an extremely loud running noise, and I'm not too sure what it could be. It's as if a car has started in the basementm, the noise is that bad. I'm going to try to switch it on again tomorrow morning, but I was wondering if there was any danger to leaving it unpowered other than maybe not having hot water. The pilot light is still on, so it seems to be going okay.