ABS unit running?

[bugs]

My ABS light comes on, goes off, comes on, goes off....

Today, I stop the car, turn it off, and there is a sound like something is running.
I open the hood and the black box that says "ABS" is humming like it's a fan.
I tap on it (gently) and it goes away.

Now I've never worked on the ABS system before and some of you might have seen how I feel about electrical issues but does anyone know if it's a soilnoid in there that's going bad or what?

Can the box be opened up and cleaned or am I looking at replacing it?
For either is there a how to on it?

I wanted to take a picture of the unit but my batteries in my camera just died. Hopefully someone will have either experienced this or knows how to address it.

Eric