Knocking/tapping sound at idle? - ModernCamaro.com - 5th Generation Camaro Enthusiasts
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post #1 of 14 Old 07-21-2009, 01:07 PM Thread Starter
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Knocking/tapping sound at idle?

OK, here's my first mysterious noise report...

I guess I overlooked this for the most part due to listening to music all the time while driving, but I've noticed almost every time when driving the car after it has been sitting off for several hours, I'll hear what sounds like someone rapidly knocking on my window for 2-3 seconds while at idle (I checked, NO ONE was knocking on my window This usually happens within 10 minutes of starting the engine and doesn't happen again for the entire time I'm driving.

What's unnerving about it is that it sounds EXACTLY like someone gently rapping on the window with their knuckles -- my first reaction still is to look all around the car. It could be the rear diff or the engine; so far I haven't been able to pinpoint it since I can't predict exactly when I will hear it.

Any clues?

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post #2 of 14 Old 07-21-2009, 01:24 PM
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Does the rate change with rpm? Does it do it sitting still, or when you're moving. Spark knock (although unlikely)??

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post #3 of 14 Old 07-21-2009, 01:33 PM
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While I haven't experienced this, My uncle pointed out a similar noise to me. It sounds almost as if the lifters are dry on start up. he only experiences this after not driving the car for a week or longer and only directly after start up.

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post #4 of 14 Old 07-21-2009, 02:58 PM Thread Starter
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Quote:
Originally Posted by el ess X View Post
Does the rate change with rpm? Does it do it sitting still, or when you're moving. Spark knock (although unlikely)??
No it only occurs once at idle (like at the first stop light) about 10 minutes or so after the car has been sitting cold for several hours. It has never happened while moving.

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post #5 of 14 Old 07-21-2009, 03:04 PM
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This is probably THE most common issue with LS engines. When cold there's a bit of piston slap. Nothing to worry about.
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post #6 of 14 Old 07-21-2009, 03:27 PM
 
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This is probably THE most common issue with LS engines. When cold there's a bit of piston slap. Nothing to worry about.
Exactly. My 01 SS did the same thing since new. Nothing to worry about
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post #7 of 14 Old 07-21-2009, 03:42 PM Thread Starter
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Originally Posted by cpiercetx View Post
Exactly. My 01 SS did the same thing since new. Nothing to worry about
My 01 Formula didn't do it, so I'm not as sure.

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post #8 of 14 Old 07-21-2009, 03:46 PM
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Originally Posted by weland View Post
My 01 Formula didn't do it, so I'm not as sure.
You can always take it to the dealer to get it diagnosed, but if you look around an LSX forum, be it Camaro, Firebird, Corvette, etc, I think you'll find this is a very common "issue"
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post #9 of 14 Old 07-21-2009, 04:06 PM Thread Starter
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Quote:
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You can always take it to the dealer to get it diagnosed, but if you look around an LSX forum, be it Camaro, Firebird, Corvette, etc, I think you'll find this is a very common "issue"
I've been doing some searching and reading and I don't think it's piston slap. When it occurs it's a tapping sound, like on glass, and it only lasts for 2-3 seconds maximum, not constant, just once. I think it's more likely to be lifter noise. I'll keep digging, but thanks for the suggestions.

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post #10 of 14 Old 07-21-2009, 05:08 PM
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Both my LS7 motors did that my first LS7 did it from new at start up when cold, After S/C cam and Exhuast was added i dont kno if it still made the noise, But was told bye several techs its a LS motor Issue and basicaly live with it,and it only made the sound when cold.

My new LS7 still makes the sound but like i said b4 only at start up and only cold,

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