It unfortunately is the ICE rpms fluctuating. The artificial audio is also a thing, but if they only did it with that, you'd also hear the engine droning a con

It unfortunately is the ICE rpms fluctuating. The artificial audio is also a thing, but if they only did it with that, you'd also hear the engine droning a constant pitch in the background. Also notice how the 'power' meter is dropping (accurately) from 100% each time.