Birds

A couple of years ago, I was sitting in my home when I realized that I was hearing some sort of noise outside.  I got up and opened the front for and saw thousands of birds in the trees in the park next door.  Thousands!  I took some pictures and a video so I could recreate the noise. So today when I heard the same sound, I knew what it was.  When I looked, however, there were not that many birds.  Still, the sound was loud.  I do not know what kind of birds they are because I couldn't get close enough to them high in the trees. Smaller than crows.  Starlings maybe?