It's subtle, but very noticeable when returning to base and landing.
Steps to reproduce:
1: Go to Mach 1.0+
2: Go to external flyby view to hear that cool boom
3: Return to cockpit view
Upon returning to cockpit view you will notice wind noise, but no engine turbine.
After landing and coming to a stop, note the lack of engine noise despite the engine still running.
100% repeatable, happens every time with those steps taken. Only seems to have this affect when going to external view and watching the flyby... hearing a sonic boom of a different aircraft from your cockpit does NOT trigger your engine turbine sound to go silent.