Here's a trick I learned recently.
Take a long screwdriver and use it as a poor man's stethoscope. Put the sharp end to a part of the engine, and the handle to your ear. It suddenly becomes very easy to isolate noise sources this way.
Now, as for rattling or clicking, it could be a number of things, from normal to very bad, depending on where it's coming from.
Fuel injectors make a sort of ticking sound. That's normal.
The timing chain and valves should not clatter, but this is fixable (I think).
Rattles from the bottom end could be rod knock, whick is the last gasp. But, your description doesn't sound like that.
