Decal and part transparency?

To add a "glass smashing noise" you will need to first, find the id of the audio (roblox), then create a script that when your ClickDetector event is fired, it will insert a sound instance into that part with the valid id. To make a decal transparent it is the same as any BasePart, simply state decal.Transparency = 1

Here is your (semi)completed code:

local id = 69; -- // Number value
local debounce = false
script.Parent.Anchored = true -- Anchores brick
script.Parent.ClickDetector.MouseClick:Connect(function()
    if debounce == false then
        local s = Instance.new("Sound");
        s.Parent = script.Parent;
        s.SoundId = "rbxassetid://" .. id;
        s:Play();
        debounce = true
        script.Parent.Transparency = 1 -- Makes Block Invisible
        script.Parent.Decal.Transparency = 1; -- // Change to your decals hierarchy position
        script.Parent.CanCollide = false -- Lets Player Walk Through Block
        debounce = false
    end
end)

This will make the decal invisible and it will play sound when it smashes.

local SmashSfx = Instance.new("Sound")
SmashSfx.Parent = script.Parent
SmashSfx.SoundId = "rbxassetid://" -- Put the id here
SmashSfx.Volume = 1 -- Change the volume of the Audio/Sound
SmashSfx.Looped = false -- Keep this false
SmashSfx.Archivable = false -- Also keep this false


local debounce = false
script.Parent.Anchored = true -- Anchores brick
script.Parent.ClickDetector.MouseClick:Connect(function()
    if debounce == false then
        debounce = true
        script.Parent.Transparency = 1 -- Makes Block Invisible
        script.Parent.CanCollide = false -- Lets Player Walk Through Block
    script.Parent.Decal.Transparency = 1 -- Makes the decal invisible
    SmashSfx:Play() -- This plays the Audio/Sound

        debounce = false
    end
end)