The only thing creepy experience I’ve had on board a train was on a late evening XC Voyager running between Bristol and Birmingham about 10 years ago, specifically somewhere between Bristol Parkway and Cheltenham Spa.
I was in carriage B alone and the door to the vestibule started fully opening and closing. After a couple of minutes, it stopped and the spotlights directly above the aisle started turning on and off, then a few minutes later, the double set of doors at the opposite end of the carriage started opening and closing. And I could just see the inter-connecting doors of the gangway start opening and closing. It felt like someone (or something) was moving through the carriage.
I did some digging a year or so later and found a Voyager had struck and killed someone on the same section of track. I didn’t note which unit I was on, but there was was a unit that had a ghostbusters sticker stuck to its outer body just below its unit number for quite some time, so perhaps it also has a reputation amongst staff!