AUDI A8 Knocking noise

[mark_jer]

I have a strange knocking noise at low revs, particularly noticeable at idle. It is a little like a playing card in a bicycle spoke, and gets quicker as the revs increase. However, during normal driving conditions, it disappears.

It is actually noticeable inside the car, but not outside, which may give a clue as to where it is coming from. However, it doesn't sound like any of the 'ticking' sounds from vents etc. that I have seen mentioned.

Is it possible that it could be a spark plug not having been tightened properly?

Any ideas please?

Thanks, Mark.

[towcestervag]

if it was a plug then you would hear it outside!
could be a leaf in the fan motor?
where is it coming from? n/s o/s centre ?

[mark_jer]

It appears to be coming from the driver's side, in my case on the right-hand side of the car!! It certainly sounds more mechanical than the fan.

[towcestervag]

cant remember where they are fitted on a8 but it could be the activated charcoal filter valve
you should be able to hear this under the bonnet at idle and will increase with revs

[mark_jer]

I just had a poke around under the bonnet. There is a panel to the left of the main engine cover, which can be unscrewed. Under this is a small round device which has two or three tubes/wires coming from it.

This appears to be where the noise is coming from.

Not sure exactly what it is, but it is certainly making noise.

[towcestervag]

thats the acf valve dont worry its the way they are