Edit: Having put more miles on the back, I'm now thinking that the difference in sound is purely down to the powerkit, and having seen some more 340 videos recently I'm.... irritated.
Last video from me, but I think the different camera angle (sorry it's in the grass, but I didn't want someone to find it and walk off with it while I was somewhere up the road!) captures the sound better:
I'm comparing to this video....