Question about 2005 Audi A6

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Loud knocking noise on 2000 A6. It was running fine until I took it in to have the serpentine belt replaced because of age. I have just under 89, 000 miles. The car is not losing power, but obviouly the loud knocking noise is a huge concern. I took the car back in to the repair shop and they did a diagnostic test and said it was the catalitic converter. My question to them was....I did not have this issue when I brought it in and NOW after driving it back home from the shop why now? Could the belt that was replaced be misaligned or in replacing created another issue.

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A loud knocking noise form the catalytic converter sounds strange, unless it was somehow damaged. Hard to say if it was the shops fault but maybe when they jacked the car up someone bent the catalytic converter. I'd take a peak underneath the car and see if the catalytic converters are damaged. It's possible that the belts are too tight and are wearing out the bearings in the pullys, but that wouldn't impact the catalytic converter. You might want to take it to another shop for a second opinion.

Posted on Oct 15, 2013


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SOURCE: A6 engine ''deep rattling'' noise

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Posted on Jan 03, 2009

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SOURCE: Audi A6 How do I replace Serptine Belt?

In response to BiTurboA6 comment, there is a full write-up at  

Posted on Apr 27, 2009

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SOURCE: 2003 Audi A4 1.8T Check Engine light on

The CEL means there is a Diagnostic Fault Code stored in the Engine Control Unit. There are 1000's of DTC's, so you will need to have it read by a Code Reader. Auto Parts stores like Auto Zone, Pep Boys, perhaps even Advanced Auto often will read the code for you; but by law they cannot clear the codes. Many codes do not cause drivability problems, severe ones will trigger the ECU to run in a Limp Mode, which would require repair work before any trip longer than a few miles. Hope this is helpful.

Posted on Jun 01, 2009

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SOURCE: 1998 Audi A4 Quattro Engine Noise

the timing is too far advanced at the time of the noise, the "diesel knock" is detonation

or this could be from using fuel with a low octane rating, try premium or octane booster.

or may have carbon build up in the conbustion chamber causing fuel to ingnite while entering cylinder

Posted on Jun 24, 2009

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SOURCE: How to replace the serpentine belt on a 06 A6 4.2?

I think you mean Tining Belt, BIG Difference. Sounds nornmal. Find a shop that does Euro Imports to compare prices, use only OEM parts.

Posted on Dec 30, 2009

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