I'm sorry it's the timing chain or timing chain guides to be precise.
there is a chain tensioner that is meant to keep up the slack in the chain, it stops holding as much tension, the chain starts vibrating and bouncing around in the engine next to these plastic rails that guide the chain and apply the tension. these guides start to crack and in some cases break apart.
the best thing to do is have the cam cover removed, have the chain and guides inspected from the top for cracking or damage and if the guides are ok, fit a new chain tensioner and hope that they aren't too damaged, otherwise all the chain, guides and a few other parts need replacing.
I'd definately try the chain tensioner first, maybe even without removing the cam cover. replace it and if the noise goes you can maybe get away with it