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Motor noise only at certain RPM

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Old Jul 1, 2011, 04:16 PM
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Motor noise only at certain RPM

Alright so my car makes a noise which sounds to me like a heat shield or something vibrating. It only occurs around 2000 to 2500 rpm. Sometimes depending what gear you are in it wont do it at all. Its almost like the engine needs to be at a certain frequency. From inside the car it sound like a heat shield but when under the hood reving it almost sounds like it is coming from inside the motor.

The car had a metal beat racing splash shield which I removed because I thought it was that. It does not seem as bad but it still does it. I have checked all the heat shields and all seem fine. The car runs great and was actually just tuned yesterday and made decent power for the limited mods the car has. It has no check engine light or anything either.

I just want to see if anyone else had a similar issue. Thanks
Old Jul 1, 2011, 07:40 PM
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I have this too, from about 2k-3k RPM. The frequency of the noise doesn't seem to change with RPM or speed though, so I don't think it's anything in the driveline and haven't worried too much about it.
Old Jul 1, 2011, 08:28 PM
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the downpipe might be hitting the sway bar above it or it could be hitting the cross bars under the downpipe. see if the downpipe is touching any one of those three bars
Old Jul 1, 2011, 08:41 PM
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Mine did this too, thought it was a wheel bearing cuz it did it when driving. Havent heard it in a while so i guess it went away.
Old Jul 1, 2011, 08:41 PM
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I remember when I went to a racing shop. Pray that it is not rod knock which I seriously doubt. Now as far as other things to check out now the timing blet it may be on its way out.

That's what I saw you can start out by checking out the timing belt take the camgear cover off and leave the car in neutral and turn the crank pully manually and maybe the timingbelt has a piece of the belt slapping up agaisnt the camgear plastic cover. Just throwing in my two cents thats all. Keep us posted also post pics if you can.
Old Jul 1, 2011, 08:47 PM
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Does the frequency of your's change with RPM/speed? I know 2-2.5k isn't a real big range, but you should be able to tell. And a different gear would tell you for speed.
Old Jul 2, 2011, 04:37 AM
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Thanks guys. I actually just had the timing belt done 2 days ago too and it did this prior.

The noise does not change with the rpm (if it does its not very noticeable). If it makes the noise and I hit the gas to put the motor under heavier load it stops. It does not seem to increase with rpm.

My fear is the noise is rod knock but wouldnt I hear the noise through a broader range of rpm's? Not just 2000-2500 rpm.
Old Jul 2, 2011, 09:14 AM
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My noise sounds almost just like yours. It's most prominent when cruising, and goes away under heavy load or decel. It's also not super loud, it's not anywhere NEAR as loud as the rod knock videos I've seen. Mine at least is a lot slower than rod knock would be at 2-3k RPM. I'd guesstimate it to be ~5hz.
Old Jul 2, 2011, 09:58 AM
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Originally Posted by Joshm3357
Thanks guys. I actually just had the timing belt done 2 days ago too and it did this prior.

The noise does not change with the rpm (if it does its not very noticeable). If it makes the noise and I hit the gas to put the motor under heavier load it stops. It does not seem to increase with rpm.

My fear is the noise is rod knock but wouldnt I hear the noise through a broader range of rpm's? Not just 2000-2500 rpm.
post a video if you had your timing belt does just two days ago just take the timing camgear cover off an dtake a look and post a video man comon dont keep us in the dark with guessing games.
Old Jul 3, 2011, 05:06 AM
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I will try to get a video up. Thanks
Old Jul 3, 2011, 07:10 AM
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Originally Posted by evo8426
the downpipe might be hitting the sway bar above it or it could be hitting the cross bars under the downpipe. see if the downpipe is touching any one of those three bars
Did you check this yet? The RPM you said it happens at seems to go right in line with the downpipe hitting any one of those bars
Old Jul 3, 2011, 11:56 AM
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Originally Posted by evo8426
Did you check this yet? The RPM you said it happens at seems to go right in line with the downpipe hitting any one of those bars
I briefly looked at it. Its a stock downpipe and the one brace that is left does not appear to be hitting it. I also noticed the car needs to get up to temperature before this rattle starts.

I think the heat causes something expand the slightest bit and that causes this noise. I just need to get some time to get under the car after it has warmed up to check this out.
Old Jul 3, 2011, 12:05 PM
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Originally Posted by Joshm3357
Thanks guys. I actually just had the timing belt done 2 days ago too and it did this prior.

The noise does not change with the rpm (if it does its not very noticeable). If it makes the noise and I hit the gas to put the motor under heavier load it stops. It does not seem to increase with rpm.

My fear is the noise is rod knock but wouldnt I hear the noise through a broader range of rpm's? Not just 2000-2500 rpm.
Your balance shaft gear spun 180* out. You need to take it back to the person/shop who did the work. They are going to have to take the timing belt back off and rotate the balance shaft gear to get it back in phase.

This happened to me back in '03 when I had to do a head gasket in my car basically in the dark with a mini mag light. I about had a heart attack when I heard the sound upon initial test drive. I would also caution against taking it to high rpm's with the shaft out of phase like this.

mitsuorder
Old Jul 3, 2011, 12:31 PM
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Originally Posted by mitsuorder
Your balance shaft gear spun 180* out. You need to take it back to the person/shop who did the work. They are going to have to take the timing belt back off and rotate the balance shaft gear to get it back in phase.

This happened to me back in '03 when I had to do a head gasket in my car basically in the dark with a mini mag light. I about had a heart attack when I heard the sound upon initial test drive. I would also caution against taking it to high rpm's with the shaft out of phase like this.

mitsuorder
I just had the timing belt and every other belt done a few days ago and it did it prior to replacing the timing belt.
Old Jul 3, 2011, 01:01 PM
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Maybe some crappy lifters! What oil you running?


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