You don't seem to be having hernia from your history.
The testis is hanging by a cord. The contents of the cord are blood vessels and nerves to penis and vas that takes away semen from testis. This cord has cremaster muscle surrounding all these structures. This cremaster muscle is very active in young children and testis remains pulled up. The phenomenon is known as cremasteric reflex. This reflex for unexplained reasons can become active at times even in adults and can pull up the testis.This reflex usually subsides by itself and the testis shall return to normal position.
Nothing active needs to be done and stop worrying about the position as well the pop sound.
Dr Rajiv Goel