Dave, You Know What Pre-Ignition Sounds Like, Right ? It's That Pinging Or Pinking Rattle Sound, Sometimes Called Spark Knock. It Behaves The Way You Describe It.
You could try a tank of premium gas and see if it helps. Does the car manufacturer recommend premium ?
If you already know all this and this isn't helping then I'll ask another question. Will it do it while idling if the car is in drive ?