Why is there a rattling noise coming from my furnace?

Sometimes it's nothing more than the heat exchangers rattling in the air of the blower. Sometimes it's something that will require some attention from a qualified air conditioning technician. Use your best judgment. If your equipment is making more noise than normal or if you're just not sure, you may be better off to have someone come and take a look at it. If you can barely hear it and the system seems to be working fine, you're probably alright.