I live in Richmond and take the District Line into Central London
about once a week. Sometimes I change trains at Turnham Green to go to
Ealing Broadway. When I am at Turnham Green, I have noticed that the
tracks make strange noises when either a Piccadilly or a District
train is approaching. No matter how fast the incoming train is
traveling, the tracks twang, rattle and vibrate like huge springs are
being snapped back and forth. Once the train has passed by, the sound
continues until the train is well away from the platform.

I have not heard this anywhere else on the Underground except at
Turnham Green and some of the stations east of it (the tracks at Earls
Court and Victoria make the sound, but it's much more faint than at
Turnham Green). Does anyone have a clue as to what I'm hearing?

Brad Chapman