Popping noise in internal wall

Bought a 1900s mid terrace last year, since January I’ve been hearing popping sounds in one internal wall, about halfway up. It maybe happens twice a day. Wall is plaster boarded (yet to take back to brick), though I don’t think the previous owners taped the boards as there is a clear horizontal line across the wall… could it be this?

Any thoughts on what it is and how I can investigate or fix?