In SC, in cooler weather, one sees large flocks of small, black, noisy birds.

[raccoon]

They walk along the ground looking for food, then they suddenly take flight to a tree a few hundred yards away.

The flocks are--I'm guessing--from 100 to several hundred birds.

What are they?

[fadedrose]

1. I would say starlings, except that . . .

right now, in winter, starlings are not black. They are deeply speckled mostly gray and black and have black beaks.

Come spring, their feathers turn to deep black and their beaks turn yellow, and they stay that way till late fall, when they start to speckle again..

They fly in huge flocks although some break off from time to time for food sources but they eventually return to the jittery flock.

[raccoon]

2. These are probably starlings. They are dark-colored but not black like crows. nt

[Curmudgeoness]

3. That sounds just like European Starlings.

That is the typical behavior for them, and they hang around in huge flocks, especially in the winter.

I know many people don't like them, but I have seen them as really smart and innovative.

[GoCubsGo]

4. They are probably blackbirds.

Rusty blackbirds and red-wing blackbirds are abundant here in the winter. The flock in huge numbers. There is a wetland near the Augusta (GA) airport, where about a million of them roost. It's possible they're common grackles, but they are a little bit bigger.

On edit: Here's a link to photos of rusty blackbirds:
https://www.google.com/search?q=rusty+blackbird&hl=en&client=firefox-a&hs=55U&tbo=d&rls=org.mozilla:en-US fficial&source=lnms&tbm=isch&sa=X&ei=lW_vUKDcIvS60AHJ14DYAQ&ved=0CAoQ_AUoAA&biw=1366&bih=589