I have a two year old, spayed cat who I've had for the last seven months. I adopted her from a shelter. Within the last three-four days she has suddenly become very vocal. She is still eating/drinking/using the litter/does not appear sick. But she has begun plaintive meows which occasionally turn into howls. She doesn't do it for long periods of time, but she does it consistently over the course of the day. She's keeping me up at night, and I'm afraid my neighbors may complain. Once before she has done something similar, but it stopped after four-five days. I never found out why. Since then she has been fairly silent. Anyone have any idea what this is/what to do about it?