As far as I can remember none of the London Underground is elevated.
Because London's transport is all integrated under control of the local government (an option which is prohibited in most UK cities to facilitate "competition" ie price-gouging by foreign owned corporations) you might not have realised that you weren't using the Underground but one of the other modes, almost all of which are covered by the same ticketing system (the "Dangleway" isn't and neither are the boats).
If you travelled on ordinary seeming trains above ground, those weren't the Underground but instead ordinary "heavy rail" trains on National Rail infrastructure within London. Many of those lines are indeed far above the ground in parts of central London, but those are just called viaducts and aren't usually considered an "elevated railway" per se.
If you travelled on small trains in East London that didn't have a driver (you can sit at the front like a roller coaster), that's the Docklands Light Railway, almost all of which is elevated, it was built towards the end of last century during regeneration of the "Docklands" area.
If the trains seemed to be sharing a road with cars at street level, in South London, that's the Tramlink.
There are parts of the Underground that are, in fact, above ground and elevated (especially farther out like Ealing and Stratford). Then there’s also the Overground, which I think counts as light rail, but is generally on ground level.
The Overground is just a (branded) part of the normal National Rail heavy rail network that serves London. Same track, same stations, same rolling stock, just operated by TFL (Transport for London) like the rest of London's public transport.
Pretty much all the elevated train lines in London were built a long time ago - often before any of the houses which surround them. I don't think any new elevated lines (with the exception of bridges and the occasional longer section to join existing elevated lines) have been built for decades, perhaps significantly more.
We have some parts of the subway in Paris which are elevated, but the street under the rail can't be used for trafic, it's usually parking space or empty. So now the city is building tram or bus lanes above ground.
I don't think that was necessary. Yes, The Blues Brothers was centred around Chicago, but it might have been a while since GP saw the film, so their memory may have been hazy.
Aside from that, The French Connection featured a famous car chase that included the elevated trains in New York City:
I'd be interested to know where you find this to be true. I have noticed that BART trains through Rockridge don't make much noise. But the track noise is so bad through Fruitvale, you can hear the trains over a mile away.
