My D750 'sometimes' has a slightly more pronounced lock on the subject, than my D600 has. Even though some of the D600's around the world had a shutter lube/shock absorbent (or whatever it was) problem, mine didn't, so I decided to keep it, yes even after I got the D750. I mean, although it didn't need it, I got the shutter mechanism replaced under the product recall 3 or 4 years ago, and today it still impresses me. It just seems to take great photo's. Why spoils things..?? When the D600 locks, it's like time just stood still all of a sudden with a "beep beep" to let you know, silky smooth, while the D750 'sometimes' has a sort of slight shunt (almost like a little jolt) to it's lock, usually more noticeable if it overshoots the mark and has to hunt a bit to find the lock. It kind of lets you know "I got it".. I can't see anything wrong with it, as it sometimes has quite fast lock times compared to the D600. Maybe it's just the share speed of its lock times that's doing it - the price you pay for speed. I mainly use the 24-120mm lens, which I bought when I got the D600,, just love this lens even though it's not really a world beater. I also use a 70-300mm and I think it might be a little more pronounced on this lens at times,, not much though, and under the same circumstances (hunting) as the above. Hadn't really noticed it too much 'til I looked at this thread... I just love both camera's and I'm so glad I decided to keep the D600 to compare them against each other. Hope soon to lay my paws on a D850,, maybe.. Fingers crossed...!!!
Nikonitus