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?