'09 C5 odd noise!

[milleplod]

My 2.0HDi auto Exclusive made an odd noise today! I was setting off from a standstill at a busy junction, accelerated sharply, and as the revs built up (presumably in 1st gear) there was a very obvious noise, just for a second, that sounded as if a valve of some sort was 'blowing off', if that makes sense. It has done it once before, similar circumstances, around 2/3 months ago.

Any ideas? It sounded horrible!

Pete

[old'uns]

If it sounded like a lollipop stick on a bicycle wheel then yes mine used to do that as well..?
i always thought it was a UJ TBH but at each service nothing to show what it was.
Got rid of mine before i got to the bottom of it

[milleplod]

If it sounded like a lollipop stick on a bicycle wheel then yes mine used to do that as well..?
i always thought it was a UJ TBH but at each service nothing to show what it was.
Got rid of mine before i got to the bottom of it

I racked my brains trying to think of something it sounded like.....yep, that was it exactly!

Pete

[petef]

Mine does it too. Think it is common with 2litre hdi's. I remember it being discussed at some length in the Citroenian if not here as well. Seems to be some kind of pre-ignition which makes the engine momentarily sound like a bag of nails but doesn't seem to do any long term harm, although I stand to be corrected.

[milleplod]

Mine does it too. Think it is common with 2litre hdi's. I remember it being discussed at some length in the Citroenian if not here as well. Seems to be some kind of pre-ignition which makes the engine momentarily sound like a bag of nails but doesn't seem to do any long term harm, although I stand to be corrected.

Ooh er...that sounds worryingly serious!! I've got to say though that I didn't get the impression it was coming from the engine itself (he says, hopefully....!), more like something low down....but I know pinpointing noise is a very inexact science at the best of times!

Pete

[Filberton]

I have similar occasionally but seem to have tracked mine to harmonic vibration of one of the engine covers. (it disappears for a while if I knock and shuffle things but then returns after a while. I found if I tried a fast pull off in first gear on an empty road I could get the noise and by maintaining the revs the period of the noise could be extended. slightly oddly, I only got the noise when pulling off on a slight up-grade not on a level or down-hill so only certain junctions.

[milleplod]

I have similar occasionally but seem to have tracked mine to harmonic vibration of one of the engine covers. (it disappears for a while if I knock and shuffle things but then returns after a while. I found if I tried a fast pull off in first gear on an empty road I could get the noise and by maintaining the revs the period of the noise could be extended. slightly oddly, I only got the noise when pulling off on a slight up-grade not on a level or down-hill so only certain junctions.

The two times mine's done it were both on slight up-gradients, so that's interesting! I'll have a root around under the bonnet. Thanks!

Pete

[white exec]

Engine/exhaust/something touching body/something else when torque is momentarily high - eg when pulling away uphill, and engine goes through its torque curve? Engine mounting will be flexible, and torque will peak and then back off. Maybe.

Or a belt "thrash" at a certain engine revs. More easily pinned down.
Or maybe hydraulic tappet racket that comes and then goes? Had this (Toyota D4D) when engine oil grade is too thin.

[milleplod]

Hmmmm.....food for thought. What about a pulley rattling?......when the aircon is on, there's a definite noise that sounds like a worn bearing or something. Tbh, its not doing it often enough to worry me....but then there's always the concern that its going to lead to something worse!

Thanks.

Pete

[GiveMeABreak]

I have similar occasionally but seem to have tracked mine to harmonic vibration of one of the engine covers. (it disappears for a while if I knock and shuffle things but then returns after a while. I found if I tried a fast pull off in first gear on an empty road I could get the noise and by maintaining the revs the period of the noise could be extended. slightly oddly, I only got the noise when pulling off on a slight up-grade not on a level or down-hill so only certain junctions.

The two times mine's done it were both on slight up-gradients, so that's interesting! I'll have a root around under the bonnet. Thanks!
Pete

Ditto Pete - on a steep hill or sharp incline I get the vibration - took a Citroen technician out once for a spin to see if he could pinpoint the noise - and said it's likely to be some protection or shielding vibrating occasionally - doesn't do it often so I can live with it.