Honda: 1997 Civic LX rattling noise, laser guns, honda parts

Question
I have a 1997 Civic LX with only 68 K miles.  I recently did a tuneup: changed the fuel filter, spark plugs and wires, rotor button, and distributor cap.  The car is in excellent shape.
Recently (about a couple of weeks ago), I started hearing a noise, audible when driving uphill.  It's like a rattling noise which increases as I press the gas pedal (but I'm by no means pressing it hard).  The noise has become more pronounced recently.  

My suspicion is that it might be the valves--they might need to be adjusted.  What leads me to that is the fact that sometimes (after driving the car for a while) the idle speed drops to maybe 400-500 RPM--and that's after we adjusted (as part of the tuneup) the idle speed to manufacturer specs with one of those laser guns or whatever they're called.  In case you're wondering who did all that, I have a good friend who is a mechanic.  

I hope this info is sufficient.  I would like to thank you for taking the time to answer all questions that me and other people have.  

Chom

Answer
    Chom,A good tune up ALWAYS includes a valve adjustment,but thats not what I think your hearing,I think what your hearing is engine ping(a.k.a. pre-detonation)ask your friend if he jumped the short connector located under the dash by the glove box before he used his "laser gun"(timing light)on your car and was the engine fully warmed up befor he did it,and if your buddy decides to adjust the valves make sure he does it when the valves are cold(under 100 degrees)ALWAYS use honda parts and re-check that timing,let me know.....Ray