What's the cause of the runway noise? Briefly, we don't know.
We don't know because the entity responsible for investigating and mitigating the jet "back blast" on the runway, the City and County of San Francisco, has steadfastly denied in court any responsibility for this noise issue.
We can think of some possible causes for the noise, however, starting with the first loud back blasts from the runway that began on or around November 21, 2015. For the first time in decades, residents had to close windows to block out what was assumed to be temporary runway sound. Slowly and steadily, the runway noise continued over the next several weeks, continuing to this day.
Airport authorities' "explanations" can probably be ruled out.
1) Airport Claim:
"There has been a tremendous increase of aircraft operations in recent years. We
are currently averaging between 1200-1400 operations a day."
From the SFO Noise Abatement Office, April 2019
The truth: flysfo.com's website said in April 2019 "while passenger traffic has grown by 36% since 2011, the number of flights at SFO has only grown by 14%" from 2011 to 2018.
2) Airport Claim: The new "NextGen" flight paths have caused the increase in noise.
The truth: The "NextGen" flight paths took effect almost a year before the
beginning of the steady, excessive runway noise.
3) Airport Claim: The runway project of 2014-2015 has not affected residential
The facts: The Federal Aviation Administration mandated that airports lacking
sufficiently long runways install sections made of a material* that stops planes
when necessary (see 2 photos below). The project began at the airport in 2014.
The return to the full use of the runways was slowly implemented until the end
of 2015*. There were changes in types of fences, their locations, jet blast barriers
(type and position) and "powerup" locations.
*Testimony of Audrey Park, SFO employee, January 21, 2020. She stated that in 2012-2014, major runway closures were for construction. Flights were phased in starting with 2015. SFO wanted 6 months of a testing period. In the first half of 2015, the runways were not fully running. They were running by the end of 2015.
Direct communications with the airport were futile; the airport repeatedly rejected my requests to talk with someone who was knowledgable about the airport's runway changes.
Perhaps the planes that face Oakland now start their "power up" (with the brakes on) 400 feet farther away from the Bayshore Freeway before starting their "takeoff roll".
The barriers that diverted the "back blast" noise up until the end of 2015/beginning of 2016 may have been replaced with a different type of back blast barrier that's no longer diverting the noise, or perhaps NO back blast barriers were re-instated since the jets now take off 400 feet farther away from the Bayshore.
Perhaps the side blast from the jets taking off on runways 1 and 28 no longer have an effective sound barrier between us and them?
Here's an anonymous interesting entry in The Burlingame Voice: