I have found that if the engine cuts in from EV mode, for the initial cycle it is very noisy with a ticking, knocking noise. If I start it in HV straight away generally it is quiet from the start
the other day I happened to start it with the accelerator depressed and the noise was there.
i find that the engine will cut in on EV mode even with some miles of range left when the temperature is below 15 deg and often it is as I am accelerating (even gently) and so it could be that if the engine cold starts with the throttle open something else is happening
to me it sounds like something ancillary to the engine (AC etc) or something is loose when cold, as once the EV goes back on any subsequent engine running is ok
i will mention it to the garage when I’m in next time but I won’t hold much hope