It's normal, at 430 hrs and 7500 miles there's been no issues with mine. It seems to sound worse after a bit of riding and the motor is a little warmer.
so put your worry beads away and ride.
I have encountered something similar when charging in the winter when the battery is below 40°F. But after things warm back up and I get a few more charge cycles completed, it's all back to normal.
I'm surprised that the predator 9500 cannot do 2 bikes simultaneously; when we do our 24hr race we use one Honda eu7000 and it can manage 2 bikes at once. And the eu7000 is only rated for 5500 W continuous.