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I have a 2008MY Fiat Grande Punto (6 speed manual transmission), which has developed what I would describe as a rattling noise during acceleration.

A few observations I have made:

  • The noise sounds like it is coming from underneath the car, at the front, approximately where the drivers feet are positioned by the pedals.

  • It occurs only when accelerating. No noise can be heard when stationary and idling, nor when driving without pressing the accelerator...

  • ... however, if I rev the engine with the clutch depressed, no noise can be heard as the revs increase, but a brief noise can be heard as they begin to drop.

  • No noticable loss in power, or degredation of fuel economy.

Checks already made:

  • The exhaust system (middle and rear sections) were replaced last year but I had the exhaust shop take a look yesterday and they ruled out an exhaust problem or a heatshield loose

  • Shop has inspected the suspension/wheels and found no problem there

  • No engine light / emissions fault codes, with several hundred miles clocked since the problem began occuring

To me it sounds like the same noise as when my flexi pipe broke, but the exhaust shop informs me it is fine.

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In my case (though a different brand) the issue was with bad transmission mounts. The car would also rattle when steering to the left. After replacing said mounts, the noise was gone. Could also be some other kind of mounts, generally the engine gets more stressed under acceleration which would result in more shaking.

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Usually when you hear a rattling noise during acceleration only, the cause is because of pre-detonation, knock, or ping (whatever you'd like to call it). This can be caused by carbon buildup in the combustion chamber, running too low of octane for your vehicle, or that that vehicle needs a serious tune up. If the injectors aren't working as well as can be desired, it can also create a lean condition which might cause this too happen.

To cure this, you'd need to get the combustion chambers cleaned, which most any shop will be more than happy to charge you an arm/leg for to accomplish. If you are the DIY type, you could also attempt a Seafoam treatment, which may or may not cure your ills. Check in your owner's manual to see what octane fuel you should be running. Depending on how many miles are on your vehicle, a clogged (or partially clogged) fuel filter in need of replacement could be restricting the fuel flow, which can also cause a lean condition to produce the symptoms you're talking about. Besides all of this, if its time for new plugs, air filter, O2s, etc, you may want to renew these.

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I found the issue, after a lot of searching through the fiatforum.com and by chance came across a suggestion it could be the intake pipe leading to the airbox, which is mounted to the chassis via a metal bracket with a rubber bushing. The bushing was worn so the plastic intake was rattling around a bit. This made a hollow rattling noise, which I mistook for the exhaust as it increase under acceleration (increased vibration through the engine, and therefore the plastic intake rattled more)

I replaced the mounting and the noise went away. You can also zip-tie the intake pipe to the bracket to reduce the vibration but this makes taking the airbox off more difficult (have to cut the zip tie every time and replace)

Plastic pipe where the noise eminates from is circled in green, place where the bracked joins pipe to chassis is arrow in blueenter image description here

enter image description here

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