I have experienced this intermittent strange double, sometimes triple clicking/rattling noise from what I think is the Turbo.

Usually happen during highway cruising, put the foot down to overtake and nothing happen until a rather loud 'click click click' noise then the turbo start to spool up. More pronounced if a fifth or sixth gear is held under manual mode and flooring it.

Doesn't seem to be doing it if accelerated from a lower gear ie: higher RPM.

When this happen it would do it few times consecutively initially on the day and then it will sort of fixed itself for the rest of the day until next time around.

Any ideas?