For me, on a phonograph disc a pop can be caused by a large piece of dust or other hard object stuck in the groove. It can also be caused by a gouge. And when the object/gouge is deep or long enough, it can cause a skip foreword or an endless repeat of the music contained in a single revolution. And yeah, these are maladies that have always plagued records. 78's were rife with them. Anti-skate adds still more tricks to the madness. It's one of the things that spurred on the development of the compact disc and other digital/computer-based playback.
