Not sure about tonight(they came down Kennington Lane before reaching you)but have noticed an increase in motor bikes and their accompanying noise in the last year. I'm not sure if its a result of the large bike shops in Vauxhall but they are a pain! As well as the noise that also race at high speeds, which resulted in a death of one of them on Kennington Lane this year.
I agree that there's a general uptick in motor bikes and the addition of the tall buildings makes the noise reverberate...but this was unusual. There were at least fifty, maybe more, bikes all in convoy. The racket was terrifying. By the way are there NO regulations regarding how much noise these animals make? They seem to rejoice in removing their silencers and deafening us all.
Many thanks jackie r & James H for info & links. Interesting to know that there is a London wide issue with bikes and noise. There is also an issue about bike rider safety as the dent in the tree outside my flat can testify to.