Class 20 "Chopper" at NYMR

On the 5th of September I went along the Esk Valley railway line to Grosmont, which is the northern terminus of the North Yorkshire Moors Railway. The reason was there was a couple of Class 20 locomotives nicknamed "Choppers". I have heard two different stories as to why they have this nickname. The first is that they sound like a helicopter when starting up and the second that they sound like a helicopter when pulling a load.
More information can be found at Wikipedia or at the Class 20 Locomotive Society.
 I got a few snaps of 20142.

Coming over the level crossing on the line from Goathland

Coupling up the carriages

Waiting for passengers