Fiesta Econetic ws cabin engine noise

[Philthy82]

Just bought a Fiesta ws econetic and everything is sweet, but I notice kind of a knock sound from the motor in the interior when it's idling.
Is this normal for the diesel fiestas? (I know diesels produce more engine noise) but this seems different. When I first heard it, I just put it down to a cold motor as they can be slightly noisier when cold.

Please let me know if your 1.6 Duratorq has this same noise