'Roaring' exhaust fault from new

Hello, Apologies if this post turns up twice. First time poster.
I have a Fiat Stilo (1.6 petrol) that since new has had what sounds
like a hole in the exhaust, but only at certain times. When the car is accelerating there is a gruff roar coming from under the car. When the car warms up, this gets much more boomy, sometimes sounding like a ripping sound. Under the car there is a type of 'mesh' that connects two parts of the exhaust together before it goes into the front silencer box, and it seems to be coming from here. If the engine is revved while still, the front part of the exhaust leading from the engine to this mesh moves, probably why the mesh is needed so it is flexible. The problem I have is that the boom isn't always there. Sometimes the car can glide along almost silently, and then the boom can just start up again later. Also, if I rev the engine while still or in neutral, there is no boom, it only happens with the engine is under load. I've took the car several times to the dealers in my area, and all are adamant that there is nothing wrong. They drive it a short distance and check its ECU, and give it back. Also, as it won't do it unless its under load, there is no boom when they stick it on the ramp and rev it. It doesn't seem to be a problem with the engine - the car doesn't really seem to loose power, it just gets noisy. Obviously as this mesh is connecting two pipes, it cant be air-tight, so could this be the problem? If I had a proplem with a leak or misaligned pipes, wouldn't it do it on every occasion (which it doesn't)? Would an exhaust place be able to check for a problem if it wasn't making this boom on the ramp? I'd love to strap up the joint so it is airtight, but obviously I cant think of anything that I could use that would not melt or go on fire!
Could anyone point me in a direction please? With the dealers refusing to look further at it I'm stuck. Sorry for a barrage of questions.
Thanks Jerry
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from snipped-for-privacy@aol.com (JerryK) contains these words:

A lot of people pay good money to make their car sound like that.
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I don't quite follow what this mesh is. If you're saying that part of the exhaust system is made of wire netting then it certainly wouldn't be gas-tight. However, there must be more to it than that because the system wouldn't be designed to leak. If it's just a piece of flexible pipe, then that shouldn't leak. Is that what you're calling 'mesh'?
Rob Graham
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On Tue, 2 Nov 2004 21:12:44 +0000 (UTC), Robin Graham wrote:

It's probably like my Rover which seemed to have a section of herringbone mesh weave armour over a thin flexi-pipe section.

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Chris Street wrote:

Yep my old primera GT had a flexi section just the same. I'd have thought most factory exhausts do.
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The best way I can describe it is that it is like a tube, about 9 inches long, connecting two pipes, but instead of being solid, it is made with many thin strands of metal hatched across each other in a type of cris-cross pattern, I presume to allow flexibility. Again, how air-tight does the link need to be? Would exhaust fumes escaping before going into the silencer give me the type of noise I'm getting, and if it is, then could somebody tell me why I'm not getting it all the time?
Thanks Jerry
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On Tue, 2 Nov 2004 21:12:44 +0000 (UTC), "Robin Graham"

Could it be a heatshield for the cat?
sPoNiX
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And here's a picture of what it looks like inside - which shows /why/ it shouldn't leak at all.
http://www.flexonics.com.au/__data/page/3225/flexible_exhaust_con.bmp
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On 6 Nov 2004 07:40:46 -0800, snipped-for-privacy@aol.com (JerryK) wrote:

After so much aggravation, personally I would take it to an exhaust fitters and request they remake the joints either end of the flexi-pipe. That is if they can't detect any gas escape with the car ticking over, which I suspect they probably could.
E-mail address, hopefully self-explanatory Andy
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from snipped-for-privacy@aol.com (JerryK) contains these words:

Ain't hard - just type flexible exhaust into google.
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