sounds like rats in the void between the ceiling and the upstairs floor!

The past couple of days, it sounds like we have rats in the void between the downstairs ceiling and the upstairs floor. The cat is at alert and a little hole (about half the size of a pencil) has formed in the middle of the living room ceiling. I don't know where to start with this one. We had works to extend the kitchen a couple of years ago and I think they most have got in through the disturbed drains. I did find a rat in the kitchen soon after and went to war with traps and sealing any holes, it seemed to have done the trick.

This time they are in a place that is not accessible. The noise can be horrendous when they are moving about. Any ideas anyone?