XC70: Engine Strange clicking noise poss from Turbo

[filbert]

My diesel 2008 XC70 (170k miles) has started making an intermittent clicking/whirring noise. It has been described as sounding like a lightweight hedge trimmer.
It lasts a few seconds and happens, eg. when I unlock the car, when I open a door, in fact it seems to be triggered by any form of electrical change.
My local mechanic (not Volvo but I have found him to be sensible and reliable) thinks it is coming from the turbo 'actuator'. Some part not engaging properly.

I do get the occasional symptoms of a misfire and lack of power but very intermittent. I did get an 'engine system service urgent' warning but it went away the day when I next I used the car.

A turbo problem makes sense and the mechanic hopes to be able to replace the actuator as the hardware seems in good order.

Does his diagnosis make sense? If so, can the actuator be replaced without the main unit?

I don't really want to take it to my local Volvo dealer as they charge a *lot* more than the local guy (and he's in walking distance)