The old Leighton Buzzard - Dunstable line with its old London & North Western Railway "Duck 8's" (0-8-0) loco's slogging up the 1/80 incline to Leighton Buzzard Station with 600 tons of chalk from Totternhoe Quarries. They had a very distinctive wheezing, asthmatic, groaning sound from their cylinders which gave them great character (although I understand from a fitter who used to maintain them that they were absolute pigs to work on, with access to the inside cylinders being very difficult!)