How to make the sound play after place ?

Have a current song variable in your code to keep track of your songs.

local currentSong = 1

Then have the variable jump up every time you switch songs.

currentSong = currentSong + 1

Complete code

local Songs = {1, 2, 3, 4, 5} -- just an example lol
local Play = true
local ID = 000000
local currentSong = 1

function New()
    ID = nil
    ID = Songs[currentSong] -- i don't want dis :I(
	currentSong = currentSong + 1
end

game:GetService("RunService").Heartbeat:connect(function()
    if Play == true then
        New()
        Play = false
        script.Parent.Parent.Background:Pause()
        script.Parent.Parent.Background.SoundId="rbxassetid://"..ID
        wait()
        script.Parent.Parent.Background:Play()
        wait(script.Parent.Parent.Background.TimeLength)
        script.Parent.Parent.Background:Pause()
        Play = true
    end
end)