Confused, why does this happen? (SetPrimaryPartCFrame)

The issue: http://prntscr.com/dnh585

Comments: If I disable the v.LightModel cframing (Z) the laser is fine, otherwise the laser top goes crazy and goes somewhere into nothingness. Help? Or maybe a explanation?

The code:

local UpdateRotation = function(Db)
	for _,v in next,Compression do
		local Data = OldPos[v]
		if Data then
			local Y_CFrame = Data*CFrame.Angles(0, math.sin(tick())/2, 0)
			local Z_CFrame = v.LightModel:GetPrimaryPartCFrame()*CFrame.Angles(0, 0, math.sin(tick())/2)*CFrame.Angles(0, 0, Db)
			v.LightModel:SetPrimaryPartCFrame(Z_CFrame)
			v:SetPrimaryPartCFrame(Y_CFrame)
		end
	end
end

spawn(function()
	RenderStepped:connect(function()
		local Db = Abs(Sound.PlaybackLoudness/130)/20
		UpdateRotation(Db)
	end)
end)