I’d say that there’s something in most locomotives are hand built and they all have little quirks and foibles?
I have a friend who’s a driver who many years ago preferred a certain Class 50 over another on the Heritage Railway he drove at, I must admit they did sound a little different.
I do wonder if there’s a bit of a ‘Friday afternoon’ element in construction, then how much care and attention something gets during construction followed up with the care and attention maintenance staff look after their Machines at certain depots?
I can imagine something like say 33008 or 47145 at Eastleigh and Tinsley had a little more care lavished on them unlike their class mates allocated to the same depots.