Hi I live at the Honor Oak end of Garthorne Rd which is very quiet due to the trsffic barriers. The last couple of days I can hear an audible "hum" a (little bit like a generator) which last night went on from 11pm till 3am at least. Audible front and back of the house so its coming from outside. Anyone heard anything similar and any ideas what it is. A mobile mast perhaps, something from the railway?

Incessant rain ?

You mention barriers - might it be assumed that there are roadworks in the area ?

If that is the case and there are also temporary lights or traffic lights in operation, the contractors may be using a silenced generator to provide power.

Unlike the old days of noisy monster generators, the modern equivalents are very much quieter.

They are not absolutely silent however and even when you were standing beside it you would hear a very low frequency hum although it may not be clear how far the reduced hum would actually transmit distance wise.

I must live v close to you...not heard any humming sorry

I live on Horniman Drive and occasionally hear a hum too - thought I was going mad. If I am, I am no longer alone !

it was probably something on the railway given the proximity to your road.