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2021 Audi S5 Sportback: Intermittent Cold Start Rattle/Noise

0

David L. · rep 0 · May 22, 4:25 AM · 1 replies · solved · Question

Vehicle: 2021 Audi S5 Sportback 3.0T Premium Plus

Hello Audi community,

I'm experiencing a strange issue with my 2021 Audi S5 Sportback (3.0T). On cold starts, especially after the car has been sitting overnight, I sometimes hear a brief, loud rattling or grinding noise coming from the engine bay. It lasts for only a second or two, right after the engine fires up, and then it goes away completely. The car runs perfectly fine after that.

It doesn't happen every time, maybe 3 out of 5 cold starts. I'm worried it might be something serious, like a timing chain issue, but the car only has 25,000 miles on it. Has anyone else with a B9/B9.5 S5 experienced this? What could be causing this intermittent cold start noise?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:25 AM

0

ClearTheCode admin answer:

The intermittent cold start rattle you're describing on your 2021 Audi S5 Sportback 3.0T is a concern that should be addressed, even if it's brief. While the 3.0T engine is generally reliable, specific components can cause such noises.

  1. Timing Chain Tensioner: This is a primary suspect for brief cold start rattles. When the engine is off, oil drains from the hydraulic timing chain tensioners. If a tensioner is weak or failing, it might take a moment for oil pressure to build up and properly tension the chain on startup, leading to a momentary rattle. While less common on newer 3.0T engines (like yours, which uses a revised design compared to older generations), it's still a possibility.
  2. Oil Filter Housing/Check Valve: A faulty oil filter housing or a check valve within the oil system can allow oil to drain back too quickly from the upper engine components. This results in a momentary lack of lubrication on startup, causing a rattle until oil pressure is fully established.
  3. Accessory Drive Components: Less likely, but sometimes a failing accessory (like an alternator, AC compressor, or idler pulley) can make noise on startup before fully engaging or warming up. However, a 'rattle' usually points to internal engine components.
  4. Fuel Pump/Injectors: In rare cases, a noisy high-pressure fuel pump or injectors can create a clatter, but it's usually more consistent than a brief rattle.

Common Causes:

  • Delayed Oil Pressure: The most common cause for brief cold start rattles is a momentary lack of oil pressure to critical components like timing chain tensioners or valve lifters.
  • Worn Timing Chain Tensioners: While improved, they can still wear.
  • Oil System Issues: Faulty check valves or oil filter housing components.

When to See a Shop: Even though your S5 has low mileage, a brief cold start rattle, especially if it's metallic, warrants immediate attention from an Audi dealership or a specialized independent shop. They can perform a proper diagnosis by:

  • Checking for any stored fault codes (though a rattle might not always trigger one).
  • Using a stethoscope to pinpoint the exact source of the noise.
  • Potentially performing an oil pressure test on startup.
  • Inspecting the timing chain system if necessary. Ignoring a timing chain-related rattle can lead to catastrophic engine damage if the chain skips or breaks.
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