Yes, RPC calls are between a replicated actor on the client and the authoritative actor on the server. For the player, this typically means the player controller.
I’m unsure on the how to play a sound in a multiplayer game, but it’s possible that you might be able to use the Multicast event from the server to inform all the clients about the sound. (Proper sound replication probably deserves a different question anyways).
As for your original question, for multiplayer games, leveraging RPC calls will likely eliminate the testing you are doing in Tick.