If you're a Subaru Forester owner, you may have encountered a persistent humming noise coming from the rear of your vehicle. This can be a concerning issue, as it often indicates a potential problem that requires attention. The humming sound typically becomes more noticeable at higher speeds, usually starting around 30-40 mph, and can increase in volume as you accelerate.

This noise is not just an annoyance; it can be a sign of wear and tear on crucial components of your vehicle. Understanding the cause and addressing it promptly can prevent more serious damage and costly repairs down the line. Let's explore the most common causes of this humming noise and what you can do about it.

SymptomPossible Cause
Humming noise from rearWheel bearing failure, differential issues, tire wear
Noise increases with speedTypically indicates wheel bearing or differential problem
Noise changes when turningOften points to a specific wheel bearing issue

Common Causes of Rear Humming Noise

The most frequent culprit behind a humming noise from the rear of a Subaru Forester is a failing wheel bearing. Wheel bearings are critical components that allow your wheels to spin freely with minimal friction. When they start to wear out, they can produce a distinctive humming or growling noise that increases with vehicle speed.

Another potential cause is an issue with the rear differential. The differential is responsible for allowing the wheels to rotate at different speeds when turning corners. If the differential fluid is low or the gears are wearing out, it can create a humming noise that's particularly noticeable during acceleration or deceleration.

Tire wear can also contribute to unusual noises from the rear of your Forester. Uneven tire wear or out-of-balance tires can create a humming sound that may be mistaken for a more serious mechanical issue. It's important to regularly rotate your tires and check for signs of uneven wear.

In some cases, the noise might be caused by a loose or damaged heat shield. While this is less common, a heat shield that has come loose can create a vibration that sounds like humming, especially at certain speeds or when the engine is under load.

Diagnosing the Source of the Noise

To accurately diagnose the source of the humming noise, it's important to pay attention to when and how the noise occurs. Does it change when you turn left or right? Does it get louder as you accelerate? These clues can help pinpoint the exact cause.

One method to narrow down the source is the "swerve test". While driving at a steady speed on a safe, empty road, gently swerve from side to side. If the noise gets louder when you turn right, it's likely coming from the left side, and vice versa. This can help identify which wheel bearing might be failing.

For a more precise diagnosis, a mechanic's stethoscope can be used to listen to each wheel hub while the vehicle is lifted and the wheels are spinning. This can clearly identify a failing bearing by the grinding or rumbling sound it produces.

If you suspect the differential, checking the fluid level and condition is a good starting point. Low or contaminated differential fluid can cause noise and, if left unchecked, can lead to more severe damage.

Fixing the Humming Noise

Once you've identified the source of the noise, it's time to address the issue. Here are some common solutions:

  • Wheel Bearing Replacement: If a wheel bearing is the culprit, it will need to be replaced. This is a job that requires special tools and expertise, so it's best left to a professional mechanic. Subaru Foresters are known to have issues with rear wheel bearings, and there's even a Technical Service Bulletin (TSB) for some models regarding an updated backing plate that can help prevent premature bearing failure.

  • Differential Service: If the differential is causing the noise, a fluid change might solve the problem. However, if the gears are worn or damaged, more extensive repairs may be necessary. Regular differential fluid changes as part of your maintenance routine can prevent many of these issues.

  • Tire Rotation and Balance: If uneven tire wear is the cause, rotating and balancing your tires can often resolve the issue. It's also a good opportunity to inspect your tires for any damage or excessive wear that might require replacement.

  • Heat Shield Repair: A loose heat shield can usually be fixed by tightening or replacing the fasteners. In some cases, the heat shield may need to be replaced if it's too damaged or corroded.

Preventive Maintenance

To avoid dealing with these noises in the future, regular maintenance is key. Here are some preventive measures you can take:

  • Regular Tire Rotations: Rotate your tires every 5,000 to 8,000 miles to ensure even wear.
  • Wheel Alignment Checks: Have your wheel alignment checked annually or if you notice uneven tire wear.
  • Differential Fluid Changes: Follow your Forester's maintenance schedule for differential fluid changes, typically every 30,000 to 60,000 miles.
  • Listen for Early Warning Signs: Pay attention to any new noises your vehicle makes and address them promptly.

By staying on top of these maintenance tasks, you can often prevent the development of humming noises and other issues that can lead to more expensive repairs down the road.

When to Seek Professional Help

While some maintenance tasks can be performed by DIY enthusiasts, diagnosing and repairing the source of a humming noise often requires professional expertise. If you're experiencing a persistent humming noise from the rear of your Subaru Forester, it's best to have it checked by a qualified mechanic, preferably one who specializes in Subarus.

A professional can:

  • Accurately diagnose the problem using specialized tools
  • Provide a comprehensive assessment of your vehicle's condition
  • Perform necessary repairs with the correct parts and techniques
  • Ensure that any work done doesn't void your vehicle's warranty

Remember, addressing unusual noises promptly can save you money in the long run by preventing minor issues from developing into major problems. Don't hesitate to seek professional help if you're unsure about the source or severity of the noise.

FAQs About Subaru Forester Humming Noise From Rear

    • How serious is a humming noise from the rear of my Subaru Forester?
      A humming noise can indicate worn wheel bearings or differential issues, which should be addressed promptly to prevent more serious damage.
    • Can I drive my Forester if it's making a humming noise?
      While you can drive short distances, it's best to have the noise checked as soon as possible to prevent potential safety issues or more expensive repairs.
    • How much does it cost to replace a wheel bearing on a Subaru Forester?
      Wheel bearing replacement costs can range from $300 to $800 per wheel, depending on labor rates and part prices in your area.
    • How often should I have my Forester's differential fluid changed?
      Subaru recommends changing the differential fluid every 30,000 to 60,000 miles, but check your owner's manual for specific guidance.
    • Can uneven tire wear cause a humming noise in my Subaru Forester?
      Yes, uneven tire wear can cause a humming noise, especially at highway speeds. Regular tire rotations can help prevent this issue.