Whenever a mob with the Silent tag set to true/1b walks, gets hurt or dies, the sculk sensor detects that even if the mob was silent.
MC-207563 Mobs with "Silent" tag can still activate sculk sensor
MC-252100 Entites with silent tag don't stop sculk from detecting them
MC-252509 Mobs with {Silent:1b} tag still emit vibrations
MC-276736 Warden can hear entities with {Silent:1b}