Sound Id doesnt work?

So i asked this question before but it doesnt work.

Ive got a script which changes the sound id and it works

Frame = script.Parent.Parent
Button = script.Parent
Text1 = Frame:WaitForChild("ID")
Music = game.StarterGui.ScreenGui.Script

Part = Music:WaitForChild("Sound")

a = Frame:WaitForChild("ID")

script.Parent.MouseButton1Click:connect(function()
    Part.SoundId = "http://www.roblox.com/asset?id=" .. a.Text

end)

But it doesnt play the song but plays the song already there.

Example

Sound1 = script.Sound
while true do
    Sound1:Play()
    wait(script.Sound.TimeLength)
end

So this Sound ID is already here "http://www.roblox.com/asset?id=151620986"but when i change it to "http://www.roblox.com/asset?id=287367450" it still plays 151620986 even when it loops around.

So im asking how would I fix this?