2020 Subaru WRX Knocking Noise? Solve Tire & Handling Issues

Overview

A knocking noise from your vehicle is one of those classic, unnerving car problems. It’s a sound that immediately grabs your attention and screams that something isn’t right. Based on analysis of 100 owner discussions, a knocking noise is rarely something you can safely ignore. It’s a symptom with a wide range of possible causes, from a simple fix you can handle in your driveway to a sign of serious internal engine trouble. The key is to listen carefully to how and when it knocks to start narrowing down the culprit.

How It Manifests

Owners describe this problem in several specific ways, which are crucial clues. The noise is often rhythmic, matching the speed of the engine or the wheels.

• Engine Speed Knocking: This is the most concerning type. Owners report a deep, metallic knocking or "clunking" sound that gets faster as you press the gas pedal and rev the engine. It’s often most noticeable at idle or under light acceleration. One owner described it as a "hammer tapping on metal" from under the hood.
• Suspension/Chassis Knocking: This knock is tied to the wheels moving, not the engine. You'll hear it when going over bumps, potholes, or when turning the steering wheel, especially at low speeds. It often sounds like a dull "clunk" from the front or rear of the vehicle.
• Tire-Related Noise: In several discussions, what was initially feared as an engine knock turned out to be tire noise. This is particularly common after switching to aggressive snow tires or when tires are worn unevenly. The noise changes with road speed, not engine RPM, and can be a loud, repetitive "thumping" or "knocking."
• Dashboard Rattle: Sometimes, the noise is less mechanical and more annoying. Owners have traced a persistent knocking to loose components behind the dashboard or in the glove box, which resonates at certain engine vibrations or road frequencies.

The Usual Suspects

Based on the patterns found in owner reports and confirmed fixes, here are the most common culprits, ranked roughly by frequency of mention.

1. Tires and Wheels: The #1 non-mechanical cause. Improperly balanced tires, separated tire belts (creating a "flat spot"), or even snow packed in the wheel well can create a knocking sound that travels through the chassis. This was a confirmed fix in numerous cases.
2. Worn Suspension Components: This is the leading cause for knocks over bumps. Worn-out strut mounts, sway bar end links, ball joints, or control arm bushings can all create excessive play, resulting in a metallic clunk when the suspension articulates.
3. Engine Issues (Serious): This includes rod knock (a worn connecting rod bearing) or piston slap. These are deep, expensive problems often linked to low oil, poor maintenance, or high mileage. While less frequently the final diagnosis in these discussions than suspension issues, they are the most costly.
4. Engine Issues (Less Serious): Engine "ping" or detonation is a rapid knocking sound during acceleration, often caused by low-quality fuel, incorrect ignition timing, or carbon buildup. It's sometimes resolved with a higher octane fuel or an engine tune.
5. Loose Exhaust/Heat Shields: A heat shield or exhaust component that has come loose can rattle and knock against the underbody, mimicking a more serious sound.
6. Interior Trim: Loose panels, glove box latches, or items in storage compartments can bounce and create a surprising amount of noise.

Finding the Problem

Diagnosis is all about isolating the variables. Don't jump to the worst conclusion first.

1. Isolate the Noise: Does it change with engine RPM (rev the engine in neutral) or vehicle speed (drive at a constant speed on a smooth road)? Engine problems follow RPM; suspension/tire problems follow road speed.
2. The Bounce Test: For suspension knocks, safely push down on each corner of the car to make it bounce. Listen for clunks as it settles. You can also have a helper turn the steering wheel lock-to-lock while you listen near the front wheels.
3. Visual Inspection: Get under the car (safely on jack stands) and look for obvious issues. Check for:
   • Tires: Look for odd wear, bulges, or objects stuck in the tread.
   • Suspension: Shake the sway bar end links, check for cracked control arm bushings, and look for leaking struts.
   • Exhaust: Gently shake the exhaust pipe and look for loose, hanging heat shields.
4. The "Screwdriver Stethoscope": For engine knocks, a long screwdriver or mechanic's stethoscope can help locate the sound. Be extremely careful around moving engine parts! Place the metal tip on different areas of the engine block and listen through the handle to pinpoint the loudest spot.

How to Fix It

Start with the simple, cheap, and external fixes before assuming internal disaster.

Start Here (Cheapest & Most Common):

1. Inspect Tires & Wheels: Check tire pressure, look for damage, and ensure lug nuts are tight. If you recently installed snow tires or new tires, have them re-balanced. This solved the issue for many owners.
2. Tighten Everything Down: Check for loose interior trim, the glove box, and underbody heat shields. Secure anything that's rattling.
3. Try a Tank of Premium Fuel: If the knock occurs under acceleration, try a tank of higher-octane fuel and some fuel system cleaner. This can quiet down engine ping caused by low-quality gas or carbon deposits.

Move to Mechanical Suspension Fixes:

1. Replace Sway Bar End Links: These are common failure points and are relatively inexpensive and easy to replace with basic tools. This is a very frequent fix for "clunk over bump" noises.
2. Replace Strut Mounts/Bearings: Worn strut tops can cause a loud knock when turning or going over bumps. Replacement requires more work but is often the solution.
3. Replace Other Worn Bushings/Joints: If ball joints or control arm bushings are shot, they must be replaced. Diagnosis here is key, as the parts and labor cost more.

Address Engine-Related Causes:

1. Professional Diagnosis for Engine Knocks: If the knock is definitively from the engine and follows RPM, stop driving the car and get a professional diagnosis. It could be anything from a needed tune-up (spark plugs, ignition coils) to severe internal damage.
2. Rod Knock/Piston Slap: There is no cheap fix. This typically requires a major engine repair or replacement.

What to Expect to Pay

Costs vary wildly depending on the root cause.

• Tire Re-balancing: $20 - $50 per axle at a shop.
• Sway Bar End Links: Parts: $30 - $100 per pair. DIY labor is 1-2 hours. Shop labor: 1-2 hours ($100-$250) plus parts.
• Strut Mounts: Parts: $50 - $150 per corner. Labor is more intensive, often 2-3 hours per corner at a shop ($300-$600+ with parts).
• Control Arm/Ball Joint Replacement: Parts: $100 - $400 per side. Shop labor: 2-3 hours per side ($200-$500 labor) plus parts.
• Engine Tune-Up: $200 - $800 depending on the vehicle and scope (plugs, coils, etc.).
• Major Engine Repair (Rod Knock): This is a four-figure repair. A used engine swap can range from $3,000 to $7,000+. A full rebuild can be even more.

Avoiding Future Issues

Prevention is always cheaper than the cure.

• Stay on Top of Maintenance: Regular oil changes with the correct grade of oil are the best defense against internal engine knocks. Follow your manufacturer's severe service schedule if you do lots of short trips.
• Listen to Your Car: Address new sounds immediately. A small suspension clunk can lead to accelerated wear of other components.
• Use Quality Fuel: Stick with Top Tier gasoline brands to help minimize carbon buildup and pre-ignition (pinging).
• Be Kind to Suspension: Slow down for bumps and potholes. Impact damage is the primary killer of suspension components.
• Regular Tire Care: Rotate your tires every 5,000-7,000 miles, keep them properly inflated, and get them balanced when new or if vibration occurs.

Source Summary: This analysis is based on 100 owner discussions from Reddit and automotive forums.