local sound = Instance.new("Sound")
sound.SoundId = getcustomasset("beautifulmusic.mp3") -- the mp3 should be in workspace folder, named beautifulmusic with the mp3 extension. you can rename beautifulmusic to something else though
sound.Volume = 5 -- the volume, 5 is the best for me
sound.Looped = false -- keep this to false or its just shit
sound.Parent = workspace -- where its stored

local character = game.Players.LocalPlayer.Character or game.Players.LocalPlayer.CharacterAdded:Wait()
local humanoid = character:WaitForChild("Humanoid")

local function checkAnimation()
    for _, track in pairs(humanoid:GetPlayingAnimationTracks()) do
        if track.Animation.AnimationId == "rbxassetid://12983333733" then
            return true
        end
    end
    return false
end

game:GetService("RunService").Heartbeat:Connect(function()
    if checkAnimation() then
        if not sound.IsPlaying then
            sound:Play()
        end
    end
end)