The bug

Non-player entities will play an event unique sound effect when applying the bad, raid or trial omen effect, even if the effect has no effect on them.

Steps to reproduce

1. Summon a pig.

   /summon minecraft:pig ~ ~ ~

2. Use the following command:

   /effect give @e[type=!player,limit=1,distance=..5] minecraft:bad_omen 300 0 false

3. Notice that the event sound effect plays even if the bad omen effect does not apply to the entity.