Knocking sound

LISASPEECHPATH

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VOLKSWAGEN

Hello,
I have a 2001 Jetta GLS, Automatic with 53000 miles. 4cl engine.
when in low speed or parked there is a knocking noise coming from the engine "just behind the glovebox". It is almost impossible to hear outside unless on a dead quiet street-and even then I don't always hear it-even when you can hear it inside the car. Also, I don't hear it above 10 mph or so- normal engine noise over rides it so I think it's still there but not sure. It appears intermittent-. Starting 2-3 minutes after turning on the car. And showing up 75% of the time I slow down/stop.
I had it checked and the tech said nothing wrong.
Any ideas what this might be?

5 Replies

P1S7OL

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45 POSTS

There could be a number of issues. Look into the following:
>Incorrect grade of fuel (I know its retarded but cannot be left out : )
>Ignition timing incorrect
>Fuel Injection System Faulty
>Improper or damaged spark plugs or wires
>EGR Valve not functioning
>Vacuum Leak
>Knock Sensor Malfunction

Hope this helps!

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Sunday, November 18th, 2007 AT 12:52 AM

LISASPEECHPATH

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3 POSTS

Thanks! I had an in depth conversation with the tech about all of this and he said that the noise I hear is really normal. It is part of the emission system and it is something creating a vacuum in the fuel line to check that the appropriate amount of fuel is being used (that I don't have a leak). He said it is intermittent b/c it checks it at intervals. And that I would hear it longer when the tank is low b/c it takes longer to check (maybe b/c it is creating a vacuum) and that it doesn't start performing the test until the car is warm. Of course I am paraphrasing all of this from memory. I have never heard of this but it matched exactly what I hear. Have you heard of it?

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Monday, November 19th, 2007 AT 12:25 PM

P1S7OL

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45 POSTS

Depends on how loud the knocking is. I should have asked you that first, but I was in a hurry to get outta work : If it is almost un-noticable unless your actually listening for it, then that could be the case. If it is very distinct and can be heard easily, then you might want to look into the afore mentioned issues. Hey glad to be of help!
Was I helpful at all? return the favor and give me some stars!

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Monday, November 19th, 2007 AT 10:06 PM

LISASPEECHPATH

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The loudness level comes and goes.I don't hear it often but when I do it catches my attention. But I am usually on a quiet street, stopped when I do hear it. I will make sure to bring it up again with your list of possibilities at my next service appt. Thank you!

You have been very helpful, unfortunately I am a newbie here and I don't have any whole points to award.I would if I could :-)

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Tuesday, November 20th, 2007 AT 11:39 AM

P1S7OL