"unknown engine noise"

my son has a 2000 zx2 with 80k miles, which has been running fine until yesterday [he just told me about it tonight]. I can only discribe the noise as if there were "marbles" rolling around in the top end. Its dark and raining here, so its somewhat hard to exactly pinpoint the origin of the sound. I guess i'm looking for someone who might know what this could be. [i'm new to 4cyl Fords].

It runs OK otherwise? Or not?

www.teamzx2.com

...son said, that it ran perfect [aside from the noise]
btw, it had a oil change week before [oil level good]

I'm gonna go out on a limb and say maybe a timing belt tensioner that is going bad, but you should be able to rule that in or out by using a wooden dowel to listen to the sound, see if it is under the valve cover, timing cover, or whatever.

Ok, now that its daylight and i can see a little i noticed that there is smoke coming up [while running] possibly around the a/c [its hard to tell-so doggone tight down there]. The a/c never worked....... do a/c bearings go bad this soon?
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update....think its the power steering pump, it seems to be the center of noise.

Take the belt off, and spin the pulleys, see which one is notchy or gravelly. I might have been closer than I thought. When an accessory bearing goes bad, the belt load will cause snapping and clicking sounds from the belt tensioner. Are you sure it is not the tensioner pulley's bearing? That's real common on GM (my weapon of choice), not sure about Ford tensioners.