April 18, 2023

Why A Furnace Makes Rattling Noise When Starting Up

furnace makes rattling noise when starting up

Furnace Makes Rattling Noise When Starting Up

If you ask, “Why is my furnace making a rattling noise?” you are not alone. This annoying and sometimes concerning sound can startle many homeowners, especially when they can’t pinpoint the source of the noise. Fortunately, understanding why your furnace produces a rattling sound can help provide some peace of mind, as it’s typically nothing too serious and doesn’t take much effort to resolve.

In this blog post, we’ll explore several potential causes and offer solutions to fix them so that you no longer need to worry about those mysterious noises from your HVAC system!

Loose or Broken Motor Mounts

When a furnace makes a rattling noise, one of the possible causes could be loose or broken motor mounts. The furnace’s motor is connected to the furnace cabinet through mounts, which helps keep the motor in place. When these mounts are loose, the motor vibrates, making a rattling noise. The furnace technician must tighten the loose mounts or replace the broken ones to fix this problem.

Dirty Blower Wheel or Fan Blades

Another possible cause of a rattling noise in a furnace is a dirty blower wheel or fan blades. The fan blades are responsible for pushing air through the furnace, and when they are dirty, they become unbalanced, leading to vibration and rattling noise. To solve this problem, the technician must clean the blades and ensure they are well-balanced.

Loose Parts or Misaligned Blower Wheel

One of the most common reasons a furnace makes a rattling noise during start-up is because of loose parts. A furnace has many small parts that can become loose from the normal vibrations of the unit. The blower wheel is one such component that can come loose, causing a metallic rattling noise when it starts up. This problem needs to be fixed as soon as possible by an HVAC professional, as loose parts can cause extensive damage to other parts of the furnace.

Faulty Inducer Motor or Blower Motor

In some cases, a rattling noise in a furnace could result from a faulty inducer or blower motor. These motors are responsible for moving air through the furnace. They may begin to make loud and unpleasant noises if they become faulty. To fix this problem, the technician must inspect and replace the motors if necessary.

Loose Ductwork

When the ductwork in a furnace is loose, it can create unwanted noise during the operation of the furnace. If the ductwork is loose or poorly fitted, it can cause rattling noise due to the furnace’s airflow. To fix this problem, the technician must re-fit or tighten the ductwork.

Dirty Air Filters

Dirty air filters in a furnace can also create a rattling noise. Filthy and clogged air filters can cause the blower fan to work harder, leading to excessive vibration and rattling noise. To fix this problem, you must regularly replace the dirty air filters with new ones.

Faulty Ignition System

The ignition system in your furnace is responsible for lighting the burner that heats the air. If the ignition system is damaged or faulty, it can create a rattling noise when starting up. A faulty ignition system could result from a malfunctioning electronic ignition or a pilot light that needs relighting. Either way, it is best to call a professional HVAC technician to fix the issue and avoid risking your furnace and home.

Aging Furnace

If your furnace is over fifteen years old, it is time to start considering replacing it. Over time, the parts in your furnace will wear down, making it more prone to breakdowns and making noises. A new furnace will be more energy-efficient, quieter, and more comfortable running than an older model.

Cracked Heat Exchanger

If you hear a rattling noise when your furnace starts up, it might be because of a cracked heat exchanger. A cracked heat exchanger is a severe problem that requires immediate attention as it can lead to carbon monoxide leaks. If you suspect a cracked heat exchanger, turn your furnace off, open all your windows, and call an HVAC technician immediately.

Normal System Start-Up Sounds

It’s essential to remember that some level of noise during furnace start-up is normal. You may hear a clicking sound when the ignition starts, a hum when the blower motor starts, and some vibration when the ducts expand and contract with the temperature change. If the noise sounds alarming or increases in volume or duration, it’s time to call an HVAC professional.

How To Fix Rattling Noise When Starting Up

  • Tighten Loose Components: If you suspect that loose components are causing the rattling noise, you can try tightening them using a screwdriver or wrench. However, be cautious not to overtighten as it may damage the component. If you feel uncomfortable handling it, it’s best to leave the job to a professional.
  • Change Filter: Changing the filter is simple if a dirty furnace filter causes a rattling noise. Depending on the manufacturer’s recommendations, filters should be changed every few months.
  • Schedule Maintenance: Regular furnace maintenance can help prevent these types of issues from arising. A professional technician can clean the system, lubricate moving parts, and inspect components to ensure everything works properly.


Rattling noise in a furnace can be a frustrating problem for homeowners. If your furnace is experiencing this problem, it is essential to determine the cause and fix it immediately to avoid further damage. Loose or broken motor mounts, dirty blower wheels, faulty inducer motors, loose ductwork, and dirty air filters are common causes of rattling noise in a furnace.

Hire a professional technician to diagnose and fix the problem, and always carry out regular maintenance on your furnace to prevent the occurrence of such issues.