I think it's the new street lights with 'Electronic ballast' giving out lots of 'mush' over a lot of frequencies because it seems to attenuate a lot of tones and I loose about 6 dB on my 'SNR Margin'
In my own case, I always since suspected that the 'flickering' streetlight was not the cause, rather that it was falling casualty to the interference just as we my washing machine and clock. But in the process of making it work, the underlying problem got fixed.
I should add it was a large new build estate, with several hundred houses added over a three or four year period. It might be conceivable that actually the local supply had simply become overburdened and switching on of street lamps was the straw that broke camel's back?
Voltage was constant and healthy mind, it was only the 'unclean' 50Hz, after street lights came on, that was an issue. Not sure if that blows my theory of overstretched supply out of the water?