Minecraft wiki entry for Exploring_an_ancient_city, associated text: If a patch has more than one shrieker, or if there are multiple interconnected patches containing shriekers, the player must act strategically. They need to be mentally prepared that as soon as they break one of the shriekers, all other shriekers nearby will be alerted, so you should surround the shrieker with wool. In the case you do activate one, destroy all of them to save time and further shrieks.