/replaceitem makes quite an obnoxious sound, which is not heard by the person whose items are being replaced.

To see this:

1. Summon an armor stand.
2. Run the command

   /replaceitem entity @e[type=armor_stand] armor.head acacia_planks

   This is quite the opposite of what /replaceitem is supposed to be. It's a technical command, and supposed to replace slots smoothly, unlike /give, which can overflow, and simply summons an item. This noise can happen up to 20x a second, is impossible to get rid of, and obnoxious in multiplayer.

This is likely WAI, but for the sake of having the option of using /replaceitem 20x a second in multiplayer, please change this.