Noisy C5 Estate

I have a 2006 C5 Estate, 2.0l VTR that becomes very noisy at motorway speeds. The garage acknowledges this, but can't offer a solution. I was wondering if there was a way around this very annoying problem and if so,
could somebody please advise me as to what I should do? Any help would be much appreciated.
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CommNet ( snipped-for-privacy@yahoo.com) gurgled happily, sounding much like they were saying :

What *sort* of "noisy"?
Engine noise? Transmission noise? Wind noise? Tyre noise?
Changes in different weather conditions? Changes on different road surfaces? Changes with speed?
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gurgled happily, sounding much like they

it's not easy to get good NVH (noise, vibration, harshness) characteristics in an estate - generally they tend to be quite "boomy". Unless suitable analysis and development is carried out during the design and validation phases, it's not an easy thing to put right after the fact ...
as Adrian says, what type of noise is it? there may be some tweaks you can perform that weren't cost effective for Citroen to do themselves ....
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First of all, many thanks for your replies. The noise is a very loud and deep roaring sound that appears to come from beneath the car; possibly the result of some vibration. It starts at around 85MPH and peters out at around 105-110MPH. Beyond 110MPH (around 5000 rpm) it becomes reasonably smooth and quiet again. My business frequently takes me to the continent and very often to, or across Germany, where speeds of 90-110MPH are very common. I hope this info helps. Thanks again, Robert

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CommNet ( snipped-for-privacy@yahoo.com) gurgled happily, sounding much like they were saying :

Does it vary according to road surface?
Could be tyre noise. Has it recently started or has it always been there?
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gurgled happily, sounding much like they

Could it be a noisy engine under-tray flapping around or catching air?
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CommNet wrote:

can you /feel/ any vibration ? have you swapped the rear wheels with the spare, one at a time ? you may have a defective tyre. also, does your C5 have an engine undertray ?if so, is it secure as they hum and flap and can cause quite severe vibration if they get damaged.
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Thanks again for your replies. I can confirm that tyre and engine noise had been eliminated. The noise may vary slightly according to road surface, but it's heard to gauge since most of my driving is on motorways where the road surface does not vary that much. I had this car from new. I was running it in carefully, according to the manufacturer's instructions, so I didn't increase the speed beyond 70MPH until the first 1500 miles. I had a BX, a ZX and an XM before, but I'd never experienced this kind of discomfort with a Citroen. Could this be an inherent design problem with the C5? Thanks, Robert
/

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CommNet ( snipped-for-privacy@yahoo.com) gurgled happily, sounding much like they were saying :

I doubt it.
Have you checked the engine bay undertray?
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Well, I've checked the under-tray. It is not loose because of a missing screw, clip or clamp, however it is a big flexible plastic under-tray that I imagine the wind can play real tricks with. I found that it is held in place by just a very few screws and they are placed far apart, leaving wide gaps for the plastic tray to rattle freely. I've added one extra screw in the middle at the front of the tray, closing a very wide gap. I think this might have just done the trick. Thanks again for your advice.
gurgled happily, sounding much like they

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I had the same problem with my C5 estate. Until it built to a crescendo, then splat ! The undertray dissapeared, fractured & fell off, at about 100 mph or so. No more noise. I'd take it off if i were you. Mine is fine now. Cheers. Ray
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<snip>

8-)
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