Rattling noise from engine. About to break down?

[Uten]

Yesterday my Yaris 2007 model started to make clacking noises from the engine. I'm always oversuspicious to new unknown sounds from the car.

Sounds like something is hitting the interior wall clonk, clonk, clonk. It could remind me of the clicking sound you get in a ford fiesta mk I from the taps that hit the valve rods.

I fear something is really wrong in the engine. It is worst at low rpm.

So my questions is. Anyone driving around with such sounds in their Yaris?
Will timing chain make noice before breaking?
How about the water/cooling pump?
Will the ac unit make such sound before giving up?

Any experience you can share in this regard?

ps: I have parked the car until I can figure it out