Apart from the gentle clicking as your unit begins and ends a cycle, you should rarely, if ever, hear a sound coming from your furnace. For that reason, if your furnace sounds like a bunch of bolts rattling around in the back of a pickup truck, you need to schedule a residential heating repair service right away. Failure to do so can result in small issues becoming major problems down the road, so getting it taken care of now will ensure that you keep more money in your pocket.
Keep an ear open for the three sounds listed below. If you hear any of them, contact an HVAC company immediately for residential heating repair.
A loud, high-pitched whining sound that is coming from your air vent usually means that the motor belt is about to give way. While replacing the belt in your motor isn't the issue, accessing it is. It usually requires technical knowledge of not only the casing and the motor, but also how to remove the right components so as to install it appropriately. Furthermore, you also need to be aware of how to disconnect your furnace from the energy source so that it doesn't start back up while you're working on it.
A rattling sound in your air vents usually means that a bolt or piece of metal has broken off and is inside your air vents, and is rattling around because of the airflow. While it may simply be a bolt that needs to be attached, the sound could also be from a piece of your fan blade that has broken off and is scraping the inside of your unit as it turns. This can cause major damage in the long run, so you'll need to have a residential heating repair technician look at it immediately.
As mentioned above, a gentle clicking sound as the unit cycles on and off is to be expected. What you don't want to hear is a unit that continually clicks as it's supposed to be in operation, since that means your unit is having a hard time turning over and staying on. Over time, this can cause your motor to burn out completely, in addition to the malfunction that is causing the clicking in the first place. Since you don't know what the issue is, the best course of action is to have a technician look at it.