Noise under the hood: You have a loose belt or need to replace your belt. It is super easy to tighten them. Just check your service manual. As for the clicking, it is coming from behind the intake camshaft sprockets. I am not exactly familiar why they do this, but both of my Zs have done it.
Noise in rear & weak start: Open the hatch and lift up the rear carpet to hear if it is the fuel pump. This can cause your car to not start as fast, being the engine is not getting enough fuel. ie fuel pump is bad. Another option is an exhaust bracket or a place where two exhaust pipes come together.
Hope this helps and thanks for the video. This helps everyone get a better idea of what you are experiencing.