The Knocking Inside The Wall

I was standing in the diningroom earlier today and I heard this knocking on the wall. I thought maybe that the knocking was coming from the neighbors, as sometimes it does. I listened closer and moved closer to the area the knocking was coming from and it was not the neighbors, it was coming from the wall between the kitchen and diningroom,wall behind the sink. I don't recall something like this being that distinctive and loud,so apparently something new or just stronger or just starting to show what it really got.