Beecroft Rd backs on to the Catford Loop lines (double track) and there is a moderate but not huge amount of freight. That includes Channel Tunnel traffic, which currently means something like 3 or 4 trains a day in each direction at the moment, including a couple at night. If Channel Tunnel traffic were ever to pick up, this could increase greatly, especially at night, where there are currently a large number of unused paths.
Howson and Kneller rds back onto the main line between Brighton and London Bridge which doesn't see much freight traffic but it is quadruple tracked and has a very high frequency of passenger trains, one every two or three minutes at times.
How disturbing the noise is, depends on things like what height the house is relative to the tracks, how fast the trains are going at that point, and significantly whether there are points and crossings in the track - trains passing over crossings at speed are significantly noiser than those running on plain track (electric passenger trains on plain track are pretty quiet). This issue with crossings means that two houses, same distance from the track, but at different points along it, might have quite different experiences.
I live backing onto a railway line - electric passenger trains are hardly noticeable at all (guests often remark on this), heavy freight trains can make more noise and even make the house shake with stuff moving around visibly, but you get used to it and I don't generally find it disturbing. If the frequency of heavy freight at night were to increase a lot, it might be different.