Causes That Can Probably Be Ruled Out
On or about the evening of November 21, 2015, some of us heard an extraordinary runway back blast roar. For the first time in decades, we closed our windows to block out runway sound.  Perhaps due to the holidays swirling around us, traveling, and the winter chill requiring us to close doors and windows, we weren't aware of the noise again until early spring 2016 when we slowly realized the back blast wasn't a temporary issue. 
Because the back blast established itself relatively quickly, we think it reasonable to rule out the following airport "explanations":
An  increase in aircraft arriving and departing SFO that, according to the SFO website, has grown 14% between 2011-2018.
Inversion layers
Wind patterns
Change in runway use
The new "NextGen" flight paths (that took effect almost a year before the steady, excessive runway noise began)