Hi Emily and welcome to the forum family!
Fireplaces....tricky little things they be. One thing to check, is anything up in the chimney portion? Working or not working, many times animals decide it's the perfect place for building a little home for themselves. I've had everything from birds to raccoons set up shop in them. You have to rule out the physical possibilities before you can look at the paranormal. One time had squirrels throwing nuts down the chimney.
Popping noises have been associated with apports....that's when items are transported from one dimension to another. Popping noises have also been noted when an entity wants to get attention....much like "knocking" noises can be heard.