Hi again Nodge, would that have power with ignition off? Is that the item on the back of the HP pump? TBH using a tube as a stethoscope Im pretty sure its the alternator. Thanks again for ideas.
The HP regulator is modulated for a while after the ignition is turned off, to bleed the pressure out of the rail.
I've never heard of an alternator making a noise when it's stationary, but I guess it's not impossible.