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I recently installed a Stage II exhaust on my 2005 Elise (and I love it). However, now there is a funky sort of buzzing resonance from the exhaust, but only at the very lowest RPMs (approx. 750 at idle). While sitting at a stop light, for instance, the sound disappears if I only add about 100 or so RPMs.

Rather than trying to shake down the entire system to get rid of this noise might it be easier to just bring up the idle setting a touch? Will there be any unintended consequences of messing with the base setting?
 

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I recently installed a Stage II exhaust on my 2005 Elise (and I love it). However, now there is a funky sort of buzzing resonance from the exhaust, but only at the very lowest RPMs (approx. 750 at idle). While sitting at a stop light, for instance, the sound disappears if I only add about 100 or so RPMs.

Rather than trying to shake down the entire system to get rid of this noise might it be easier to just bring up the idle setting a touch? Will there be any unintended consequences of messing with the base setting?
I believe your idle is controlled by your ecu, so I'd suggest finding the rattle instead.
 

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Forget the idle.

Go back to the guy who put in the exhaust and tell him to fix it.

It's hitting something back there...or it broke. Mine had to be re-welded.

Been there, done that.
 

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Discussion Starter #5
Go back to the guy who put in the exhaust and tell him to fix it..
That would be me. ;)


Actually, it does not sound like anything is "broken". It's just a weird noise (I know... it's a Lotus) that is more of a resonance. These things occur when competing sound oscillations overlap. Nothing is banging, clanging, or scraping, and once the car smooths out just a little with more RPMs, it is completely gone.

900 RPM idle is probably correct for the base... the tach does not have any precise markings down there.

I suppose I'll just live with it.
 

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Take a look at it if you can. Mine was rubbing right where the tips come out AND there was a small hole that had to be re-welded.

That fixed that noise.

My car has a resonance point too at low revs, but it's more of an engine thing.

I just would NOT mess with the engine idle.
 

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Discussion Starter #7
Thanks Larry, I'll take a closer look.
 

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Look what happens, I go to college and he messes the car up.... :thwack:
 

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Oh, and now that I think about it, take off the rear drivers side wheel and the wheel liner and check the heat shielding that covers that 180 degree bend. That bolt might have loosened.
 

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This is that moment in any car's history when you start to disassemble the entire car to find one stupid irritating noise.

This is the moment, for any car, when you take your car to a trained mechanic and let them listen.

Why drive yourself crazy?
 

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My guess is the same as Larry's. The tail pipes are probably vibrating against the aluminum where they protrude from the car. I'm not sure about the Stage II exhaust, but a lot of the aftermarket exhausts tend to drop a little over time and begin to rub.

With the car running at idle, it should be pretty simple to check to see if this is the case. If it is, you have two options: loosen the exhaust, move it up a bit, and retighten OR get a slightly bigger opening cut out for the exhaust. After doing the first a couple times, I opted for the latter.
 

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Or check the back of the canister to the heatshield. Or check the diffuser bolts, the two larger ones loosen up and will allow a low freq rattle.
 
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