As I stated on another thread similar to this one,
v., droned, dron·ing, drones.
1. To make a continuous low dull humming sound: "Somewhere an electric fan droned without end" (William Styron).
Drone is totally subjective. To one person a certain exhaust may have no drone but to others it may have drone.
The Active Autowerke Exhaust has Noise Cancellation chambers on the side of the mufflers to reduce "drone".