I have one too. I've had Pearl since she was a kitten and she almost always has to meow loudly when she's using the litter box. At first I thought that she was in pain but no she just wants everyone to know that she's either going pee or poo. Pearl is also a very chatty cat but she is a Lynx Point Siamese mix.

Now Sky will do the scratching on the sides of the litter box and I some times have to tell him that's he done and to get out of the litter box. He'll some times do this late at night or in the wee hours of the morning while I'm trying to sleep. I have 2 litter boxes back in my bedroom now.