Why does a pylon hum.....
... because it doesn't know the words.
A busy day with not much chance to blip (this must sound feeble to anyone in a full time job!) but I had a bit of time to kill whilst waiting for a train. The rainbow I wanted had just faded, so hope you don't mind a pylon instead.
Apologies if I've not been able to reply to everyone, but many thanks for your comments etc.