This melody is unique (on London Underground) to the Jubilee line.
Although the Northern line trains have an almost identical body design, they use a more modern IGBT traction system which, although presumably more efficient, has a little less character!
Yes, the 3-phase synchronous AC locomotives driven with IGBTs seem to be quieter.[1] But the real advantage is precise wheel control. Here's the biggest steam locomotive ever built being towed out of the Pomona Fairgrounds for restoration. They're towing it through a very tight turn on temporary track to get it out.
The locomotive doing the towing is a 2006-model Electro-Motive Diesel-electric locomotive. It's towing the old steam locomotive at a very slow speed, smoothly, with no wheel slip. Nothing special about it; Union Pacific has hundreds of them. Six axles, each powered by its own motor. AC synchronous, IGBT power control. The motors are run as servomotors, all locked together. No wheel can slip relative to the others. This is a huge win when you need to get a few thousand tons moving.
This boring but useful modern locomotive, although much smaller, has more drawbar pull than the Big Boy. Multiple locomotives can be ganged together with wheels locked in sync, if you need more pulling power. Here's Union Pacific overdoing that.[2] They put together a train 3.5 miles long, with 9 locomotives spaced throughout the train, and ran it from Long Beach to Denver. This was just a test; they don't normally run trains that long.
All this is made possible by modern electronic motor controls.
There are some trains on the London Underground that use gate turn-off thyristors, which make a sort of Star Trek klaxon sound when they start up:
https://www.youtube.com/watch?v=pagB58tGpRY