Clicking sound just after start up..

[aerodynamica]

Each time I start the C5 from cold there is an intermittent ticking sound from somewhere in the engine area. No idea what it is or if it's the sign of a new failure to come. It sounds a bit like the click of an air conditioning compressor clutch but this has clicks in rapid succession for about 10 seconds. Turning off the A/C doesn't change it. It seems to stop the sound and it doesn't seem to return at all afterwards.

Bit of a vague question but thought I'd ask in case someone recognises the symptom.

This is a 2.0 HDi Auto with DPF.

[GiveMeABreak]

There are various clicks and whirring sounds. These can for example be the electrical relays switching in or out, the EGR self-clean function operating etc., ort the suspension BHI settling down. The whirring noise may cease once the BSI has gone to sleep and closed the main networks down.