Strange sound when engine switched off

[Bootstrap]

Thanks for the link Paul, however this elusive sound still persists even after replacement of the filler vent valve.
I've noticed the sound when driving and it seems to be occurring at regular intervals of a few seconds on and then repeats maybe 30 seconds later.
It only happens when the car is hot and naturally can not be heard when the car is stationary making it difficult to precisely locate.
I'm thinking that this may be related to the vent circuit associated with the plastic tab that is engaged when the fuel cap is fully installed.
This sound was not apparent when a non genuine fuel cap was fitted to the car.
It has only been audible since a genuine cap was recently installed by a repairer.
Is there another location or component that may be responsible for this unusual problem?
TIA

[Bootstrap]

For the information of members, the noise was traced to a faulty non return valve adjacent to the charcoal canister. A similar Audi unit did the trick at a total cost of $4.00.

[Starter986]

Originally Posted by Bootstrap

For the information of members, the noise was traced to a faulty non return valve adjacent to the charcoal canister. A similar Audi unit did the trick at a total cost of $4.00.

Awesome! Great detective work... and $4 later!

[NewArt]

Originally Posted by Bootstrap

For the information of members, the noise was traced to a faulty non return valve adjacent to the charcoal canister. A similar Audi unit did the trick at a total cost of $4.00.

And thanks for updating!