My father is visiting me in sf from hawaii. he's constantly getting a popping every 20 seconds or so similar to a pressure gradient. he's in relatively good health?

In ears?: I must assume the popping is in his ears and that he flew recently to SF. Air pressure at flying altitude is low which causes expansion of the middle & inner ear and Eustachean tubes. During descent, these spaces can collapse and trap air and/or moisture in them. Until the air pressure reaches equilibrium inside & out, he may experience "popping" when swallowing or yawning.