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Discussion Starter #1
Hello everyone. I am the latest owner of bone stock 2007 Exige S in Ardent Red. Among the many creaks, rattles, and other unsettling sounds which my car makes, most of which I have come to terms with, there is one that has gotten under my skin. I'm hoping you all can help me track it down, since there is no lotus dealer where I am located (Cincinnati, OH).

This noise is a prominent buzz which starts with a quick crescendo at 3000 RPM and subsides pretty abruptly at 3500 RPM. It sounds like it is coming from the passenger side of the engine. It occurs both on acceleration and deceleration, in gear and out of gear, clutch in and out. It is not present when the engine is cold but starts after a few minutes of driving. I have scoured the forums for possible culprits, but nothing seems to fit exactly. I understand that common culprits include a cracked support bracket between the block and the exhaust manifold, the exhaust tip rattling against the diffuser, and a resonating piece in the transmission crossgate linkage, but none of these fit my scenario.

The car has 45K miles on the clock, 15K of which are track miles. Aside from this noise (and a slow oil leak that I presume is from the timing chain tensioner), the engine runs great with no loss of power. The noise detracts a lot from the driving experience, since I spend most of my time in the 3-3.5K rev range. If anyone can provide any insight at all into what the cause may be, I am all ears!! Thank you in advance.
 

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Check your belts and all brackets. They are all on that side of the car. Make videos and move your mic around so that changes can be heard. Better yet secure a cam back there and move around while recreating sound.
 

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Discussion Starter #3
I’ve read that the bolt holes on the alternator can become ovalized and rattle, but I wouldn’t think a buzz from an accessory would be engine temperature-dependent. This quality makes me suspect either something in the exhaust or in the valve train.
 

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Early aftermarket brackets for alternator and SC have had problems in the past and while this is OEM it wouldn't hurt to check. Sure sounds like the exhaust crack problem.
 

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Undertrays tend to vibrate at that range, so have you checked them? As a "pre flight test", I always walk around the car and tap them with my knuckle. It is a clear sound difference between tight and loose
 

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Early aftermarket brackets for alternator and SC have had problems in the past and while this is OEM it wouldn't hurt to check. Sure sounds like the exhaust crack problem.
I'll check the exhaust carefully next time I have the car up on jack stands.

Undertrays tend to vibrate at that range, so have you checked them? As a "pre flight test", I always walk around the car and tap them with my knuckle. It is a clear sound difference between tight and loose
The undertrays were the first thing I checked. Last time I had the trays off, I installed new SS hardware and anti-rattle washers to no avail.
 

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I have an Elise. My undertray has sometimes made that sort of noise after I've done an oil change. If it is that, the way to solve it is to loosen all the bolts and push the undertray firmly forward. Then tighten the two 13 mm large bolts. Then tighten each of the 8 mm bolts making sure to apply a bit of pressure by hand to the undertray as you go. The idea is to make sure that it is "stretched out and flat" as you tighten it. I'd start with the center bolt at the back first, then the two front most side bolts.

I don't know if this is your issue but I've had the undertray issue a few times and it took away all the pleasure of driving my car.

The anti-rattle washers I think would make no difference. The noise is caused by the undertray being slightly "non-flat" when you tightened it.
 

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Discussion Starter #8
I have an Elise. My undertray has sometimes made that sort of noise after I've done an oil change. If it is that, the way to solve it is to loosen all the bolts and push the undertray firmly forward. Then tighten the two 13 mm large bolts. Then tighten each of the 8 mm bolts making sure to apply a bit of pressure by hand to the undertray as you go. The idea is to make sure that it is "stretched out and flat" as you tighten it. I'd start with the center bolt at the back first, then the two front most side bolts.

I don't know if this is your issue but I've had the undertray issue a few times and it took away all the pleasure of driving my car.

The anti-rattle washers I think would make no difference. The noise is caused by the undertray being slightly "non-flat" when you tightened it.
Thanks for the tip. I followed your advice and unfortunately my buzz persists. Still a useful protocol to potentially avoid more unpleasant noises down the line though.
 

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Has the identical problem with my '04 Esprit. Got under and started pounding the exhaust with a rubber mallet to find the buzz and tracked it down the back box. Couldn't see any thing so dropped the exhaust and found a 1 1/2" long hairline crack at the top of the weld where one of the pipes enters the box. A quick re-weld eliminated the problem.
 

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Discussion Starter #16
Thank you all for the feedback. Thus far, it sounds to me like the leading suspects are:

1. Cracked header support bracket;
2. Cracked header lower heat shield near bolt holes;
3. Crack in u-tube (or somewhere else in exhaust.

I should have time this weekend to drop the exhaust and take a closer look at these areas. In the meantime, any thoughts on what else I should check while I'm in there would be much appreciated.
 

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Discussion Starter #17
So I haven't found time to drop the exhaust to inspect for cracks yet, but I was able to snake a fiberoptic camera down there and look around. I can say with 100% certainty the exhaust manifold stay is not cracked... BECAUSE IT IS COMPLETELY MISSING. I know at one point a previous owner had installed an aftermarket exhaust which was subsequently replaced with the factory exhaust, apparently without the manifold stay.

I cannot be certain the lack of this piece is the cause of my noise, but that's my hunch. Does anyone know exactly what the purpose of the bracket is or how vital it is? I have one on order.
 

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Since you will be down there anyway, I'd loosen and correctly re-torque the shear panel. Will take 2 minutes. They can sometimes cause some buzzing.
 
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