You shouldn’t be able to hear the buzz of the engine as altitude increases. As air density reduces the harmonic resinance of the sound of the fan blades should dissipate. The only thing you should hear from the cockpit as altitude increases the sound of the airflow hitting the windshield. They’ve done a fantastic job of replicating this in the new version. As a pilot myself, I hope they don’t change this. It is correct. PMDG and Fenix also model this very very well.