local i = 0
local last
hook.Add("Think", 1, function()
    local t = math.Round(i)

    if t == 1 or t == 4 or t == 9 or t == 12 then
    if not last then
        local pitch = 10
        for i=1, 2 do
        WorldSound("doors/door_metal_medium_close1.wav", Entity(871):GetPos(), 100, pitch)
        end
        last = true
    end
    else
    last = false
    end

    i = (i + FrameTime() * (Entity(871):GetVelocity():Length() / 50))%30
end)