Most rats will sleep during the day and then come out during the night when people are likely sleeping.
If you have rats in your house the rat will likely stay in hiding and be sleeping during the day but as soon as you turn out the lights in your home and go to bed then you will usually hear the rats or rat come out and going through your stuff in the house.
Whenever I have rats that's exactly what happens as I will never see the rats come out in the day when I'm in the house but after I shut the lights off and go to bed and the house is quiet the rat will then come out.
A few minutes after I get into bed and am ready to go to sleep I hear the rat come out and going through stuff.
You can get rid of the rats by putting out some rat poison or use some live traps to catch the rat in by putting some food inside the rat trap cage and then kill it before you take it out of the cage.