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Old 01-05-2015, 11:49 AM   #1
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Default Strange rattle/knocking noise at 2-3000 rpm. Any ideas?

Hey everyone, so ive been experiencing this noise lately that is complete rpm related and sounds like a decent rattle or knock coming from the motor that cuts on between about 2-3000 rpm and then disappears with higher revs/load. The car is boosted and otherwise running fine on a ms3x. I cant decide where to start here and figured someone else may have heard the same noise at some point in time. Ive suspected many things from a loose nut or stud or exhaust rattle somewhere to a little too advanced ignition timing but I cant quite put my finger on the source of the problem. I dont suspect bearings to be the cause, that noise should get worse with load if that were the case. Here's a video I shot before work that captures the sound a couple of times, most notably at the very end of the video. If anyone has any ideas any and all help is always greatly appreciated!-
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Old 01-05-2015, 11:50 AM   #2
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Last edited by Braineack; 01-05-2015 at 12:41 PM.
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Old 01-05-2015, 12:10 PM   #3
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Pretty sure that's your exhaust on the subframe, front or rear depending on clearances. I'm guessing you'll hear it under cornering too.
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Old 01-05-2015, 12:41 PM   #4
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how do you know what RPM the rattle is at?
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Old 01-05-2015, 01:02 PM   #5
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Shadow dash or tunerstudio. Just didn't have either hooked up at that particular moment.

And I dont really hear it under cornering, its pretty rpm specific but I do sometimes hear it when I shut the engine off.

Thanks guys.
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Old 01-05-2015, 01:15 PM   #6
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Yeah that's exhaust touching something. You have a resonance at 2-3000rpm, and another sometime between idle and 0 rpm. If you're not hearing it from 3-7000rpm, you'd probably hit another resonance at higher rpm, but most likely you'd also start to hearing rod knock.
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Old 01-05-2015, 03:28 PM   #7
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Its not very clear from your video, but if it is an exhaust related rattle as Curly is suggesting, then it might be one of the cat heat shields.

Mine rattled when one of the corner spot welds broke. Its hard to tell from looking, but you can tell easily by moving the heat shield at each corner (both top and bottom pieces of the shield)...Don't try it while its hot though...
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