Sound script won't stop music?

I have this in a localscript:

local player = game.Players.LocalPlayer

local music = player.Backpack.Inside
if player.Backpack:FindFirstChild("Outside") or player.Backpack:FindFirstChild("Outside2") then
if player.Backpack.Outside.IsPlaying == true then
player.Backpack.Outside:Stop()
elseif player.Backpack.Outside2.IsPlaying == true then
player.Backpack.Outside2:Stop()
end
music:Play()    
end

It's supposed to stop playing the sounds "Outside" and "Outside2" in the Backpack and play "Inside" instead. However it doesn't stop "Outside" nor play "Inside". Any ideas?