Resonate clatter at 3,800 RPM

[Ben Fenner]

It happends under load or in nuetral. When under the hood it sounds like
it's coming from the cam gears or timing chain inside the valve cover. I'm
not sure what's going on, it couldn't be a bent valve could it? I don't
think so, because it only makes the sound at this one rpm range. If I rev
the engine to 5k or so and let the rpms fall, like clock work the clatter
happends around 3,800 and then imediately stops again. I wish it were the
exhaust manifold heat shield or something, but it's not.
Any ideas?

On a side note, the engine looks like it's leaking oil from that side of the
valve cover gasket area as well.

-Ben
1994 Sentra SE-R (with 1994 G20 engine of unknown millage)