Since there are two children now, they must compete for attention. Baby has already learned that to win the attention contest, she must be loud. When she first came home, she cried mildly for attention. She quickly figured out that I can ignore that while taking care of Kiddo's needs. Now she whimpers a bit, then starts crying loudly and persistently. She's figured out that to get the attention she wants, she must make some noise.
Interestingly enough, Kiddo has learned the same lesson. Two days ago when she was upset she cried for 30 minutes straight, to ensure that I focused on her, and her alone.
I'm grateful that neither one of them is prone to crying, so they only push the volume up (make the noise big) when they're serious.