What is that whirring sound that comes from beneath London Underground trains, whether moving, or stationary?

Question

What is that whirring sound that comes from beneath London Underground trains, whether moving, or stationary?

Answer 1

Aliens preparing an invasion.

Answer 2

air flowin through the tunnels

Answer 3

I believe it is the electric motors and the cooling fans that prevent them from overheating that make that constant whirring sound.

Answer 4

An American engineer trying to figure out why the British system is so successful.

Answer 5

Its the air moving around from the sunction of the air down into the underground

Answer 6

yeah the london trains make a lot of noise when you're in them whether you're moving or not...I think its just pressurized air flow beneath the train.

Answer 7

That "whirring sound" is from compressors which provide air for the train to run and (more importantly!) stop. These work periodically, usually after the train has arrived at a station using air from the reservoirs to brake and work the doors although they can come on at any time according to the air requirements of the train.

There is another piece of equipment which makes a whirring noise, and that is the motor-generator - and on more modern stocks this is a motor-alternator. This provides low voltage current for lighting and most of the control circuits throughout a train.

As to all of the other answers given so far, I shall make no comment.....! ! !

Answer 8

The incredibly un-affective air-con

Answer 9

It could be mice listening to their i_pods...