Brad Chapman:
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 [or leaving]. ... the tracks twang, rattle and vibrate
like huge springs are being snapped back and forth.

Does anyone have a clue as to what I'm hearing?

On some parts of the Toronto subway system, oversize concrete sleepers
are used. These are so wide that they form almost a continuous sheet
of concrete with only small gaps between them, and although the rail
fastenings are spaced as usual, each rail is fastened to each sleeper
in two places. I have heard that between these sleepers and another
layer of concrete underneath, there is some sort of rubber; I don't
know in what form exactly. And this track makes sounds very much like
Brad's description, except that I would have omitted the word "rattle".

So do the tracks around Turnham Green *look* any different than on
other parts of the Underground, these days? It's been some years since
I was there.
--
Mark Brader "Never re-invent the wheel unnecessarily;
Toronto yours may have corners."
-- Henry Spencer

My text in this article is in the public domain.