Nobody enjoys going into a dark basement when there are frightening sounds coming from the furnace. Here are some likely sounds that might be making the noise. If you hear a loud ‘boom’, it’s usually caused by a delayed ignition. An Heating plus A/C supplier should be called immediately since the cause could be an explosion from gas building up in the furnace chamber. The same sound occurs when too much gas builds up when lighting a gas grill. There are numerous explanations for why ignition is delayed in a gas furnace. One is that there is a high air-to-gas ratio, making the ignitor taxing to light. Another cause might be insufficient amounts of gas due to low gas pressure. Finally, the burners could be jammed with debris, worn down, or otherwise compromised. Another sound coming from the furnace is more love a house-shaking rumble as the furnace completes one of its heat cycles. This cause is truly due to the fact that oil continues to burn in the combustion chamber after the burners shut off. Again, call a certified Heating plus A/C repairman immediately. This concern can lead to carbon monoxide gas being released into the home, which is deadly. If the furnace makes a loud rattle when it clicks on, carbon monoxide could also be the culprit. The furnace may have a cracked heat exchanger, which is the biggest cause of carbon monoxide leaks. Next are squealing or grinding noises, the cause which more than likely is a loose blower belt. Or, the motor bearings could be failing as well as need to be replaced or oiled. A clicking noise is normal when a furnace first turns on, which is from the ignitor. Finally, a buzzing noise is truly the result of something that’s loose in the furnace transformer.