You can use the
stopsound @s mob.evocation_fangs.attack
🧰 The Command
stopsound command can be utilized to, stop sounds. The syntax for this command in Bedrock Edition is:
stopsound <player> [sound]
player is required,
sound is optional, per DigMinecraft:
player is the name of the player (or a target selector) that you wish to stop the sound effect for.
sound is optional. It is the sound effect to stop. (See List of Sound Effect Names.)
🔊 Evocation Sounds
There are several sound effects related to evocation:
The one you're interested in is
You'll need an additional command block, set to always repeat unconditionally, at a faster rate than your summoning command block. This additional command block should have it's command set to:
stopsound @a[r=5] mob.evocation_fangs.attack
This was my setup:
You can remove the radius argument if you'd like, I just limited the command to all players in the immediate area.
📑 Final Note
Unfortunately, chaining the command block isn't fast enough as the sound effect has enough time to trigger before the secondary command block. While it will muffle the sound, it won't eradicate it unless it's a separate command block with a faster rate than the summoning.