First started hearing at 1k but the noise comes and goes... and it's a loud "clack" rather than a dull clunk. But I also ride with my windows open. I suspect it has to do with how I "land" on the joints when I release the clutch. There's too much slack somewhere in the drive train. How fast or slow it's moving has no impact. How "smooth" the clutch release is, has an impact. New, the axle shafts were rusted when everything surrounding them was bright and clean. If replacing the axle shafts has no impact, then it has to be internal to the differential/transmission... which reminds me that I've wanted to swap out the factory trans fluid. Anyway, if we start to get reports about axle shafts breaking, we'll know. Until then, it just remains a noisy embarrassment that in ignorance to observers, may be chalked-up as, "there goes another Powershift Transmission...".
I *really* have rev the living snot out of it get any rear motor mount contact and therefore have no plans to mess with that. No out-of-the-ordinary noises, either in occurrence or volume when shifting into first at a stop. There's barely any noise at all under those circumstances.