What is this sound?

What you're hearing is the wingtip vorticies. A really powerful one sounds
like someone ripping a bedsheet in half.

My office used to be adjacent to the final approach to Rwy 7 at KSBA, and
I have observed this phenomenon on numerous occasions. Often a sound like
fabric being torn. There was a row of trees parallel to the approach, and
these would often be thrashed about violently when the vortices hit them.
There was also a corrugated steel "vanity wall" (to hide the air conditioning
equipment) on top of an office building - likewise parallel to the approach.
Often the vortex striking this structure would make a sound like it had been
hit with a sledgehammer.

I know that there are those hereabouts who will dispute this, but it is my
observation that airplanes with winglets produce more violent wingtip
vortices than those without.

David Johnson