Phil R,
The exhaust peaks you site are very close to mine. What I have noticed is at 2000 rpm the exhaust is relatively quiet. At 75-80mph and 3000rms the exhaust is quite loud. The X needs another gear or a lock-up torque converter to bring the rpm down to around 2500.
...at around 2,500 rpm which is a rich mid tone (almost a 60-cycle hum).
60Hz hum is a good way to describe the sound but a rich mile tone?
A 60Hz hum is any thing but rich and mild, particularly at high volume over a period of extended drive time.