Submarines are (almost) always in total stealth mode. This started during the Cold War. Soviet and American subs would track each other and try to find each other while avoiding detection themselves because total global thermonuclear war could start like...any second and knowing where the enemy's ballistic missile submarines were was not something you wanted to wait on. Keeping submarine locations secret is so important that even commanders didn't know beyond a vague area they were ordered to patrol.

Active sonar (the pings) is rarely used in general, as it's sort of like sneaking around in a forest and turning on a spotlight. If you've been seen but you don't know where the enemy is, it is worth shining it around, but if you have no idea where the enemy is, active sonar gives away your position at a much further distance than it reveals enemy positions. Instead passive sonar is used, listening for the displacement of water by the hull and propeller.