Physical grinding would show some wear on the rods quickly, and I see almost no wear on mine. While I had converted my Mk4 to CoreOne+, so these are the same rods.

Also, some printers are more quiet than others, some steppers louder some more quiet (my X and Y stepper are fairly different in the noise they generate but it doesn't affect print performance). There's a lot of variance but it doesn't seem to mean much. 

"Stealth mode" is the solution if you need to keep volume down. Otherwise, aggressive moves will be noisy, it's in the nature of stepper motors: Two coils cancel each other interpolating between steps along the rotational axis but there are other axes where the forces aren't orthogonal and therefore don't balance out.

Generally, quiet operation comes at the expense of performance (=> stealth mode)