From engines or from sonic booms? I think this is to make take off quieter for personnel and people in the vicinity of activity ANG/airbases. SF flyovers going after incursions occasionally have booms.
When was the last time a military airplane actually caused a sonic boom near SF?
Growing up in Kansas in the 60s, I heard window-rattling sonic booms all the time. I enjoyed them :-) I'm sure the pilots were having a good time, too.
Here's a recording of the F-35 making one in 2019, and this also serves as a reminder to all San Francisco residents that fleet week is coming up. I don't think they'll get these upgrades installed in time, which sucks for anybody that lives here that hates disruptively loud airplanes, however.
Notice the gradual fade-in of the sound. That's not a sonic boom, those are a sudden pressure change with lots of sound waves packed together in a single wavefront.