2003 Mazda6s Engine Rattle?

[Prodigy]

I'm trying to help a friend who has a 2003 Mazda6s.

I am having some odd engine noise lately.
It's a long rattle at start-up and it goes away after a few minutes.
It's sounds more of a metallic rattle as if a rock got thrown up in the engine.
Today, it almost didn't turn over and it almost locked up.
Then, it did the knock when I turned and parked in a space.

Does anyone know of any common problems that will point me in the right direction?
I'm going to go look at the car in a few hours.
(My best guess would be the timing chain and/or tensioner but I haven't found a thread relating to the 2003 model)
Thanks in advance.