What are the differences between I am on it and I am at it? What does the latter mean? I found the definition of the former on Urban Dictionary and understand that it means I'm going to solve it shortly. For instance:
A: This guy is making noise and I cannot concentrate on my work.
B: Don't worry, I am on it.
I've also heard:
Oh, those reds are at it again.
in the context of a feud between reds and blues. Googling did not help.