Well it's not really grinding. That's just the closest description I could come up with at the time.
Since then I recorded it and have been able to listen to it multiple times.
It's probably closer to the sound when you put the trans into park while still rolling. Though not as loud.
like dragging your finger across the teeth of a comb
That actually descibes the sound pretty well.
I doubt anyone could blame a solenoid pack in regards to grinding on engine shutoff.