for a while now my car has made a very faint clicking noise. its loudest at idle and goes away when i rev or just drive it then back to clicking at idle. not sure if this is just a coincidence or not but it got louder after my last oil change. yesterday i put on new spark plugs wires and noticed the prong closest to the passenger on the coil was black and had a little rust on it while all the other ones are still shiny...could this maybe be causing misfire and making the noise? how would i know if its knock? TIA

How does the car run?

If it was backfiring, you would get a CEL.

Probably your lifters ticking, as they are prone to do on our cars when they are getting older. Pop the hood and start the car, find out the source of the noise.

Push down on the spark plug tubes and check to see if there's a strong bouncing on it. My #2 plug is doing that. I assume it's changing the plug or the gap but i'm new to these cars so i'm not sure.?
Could be a possiblity to the ticking if it is not the rusted bit.
Hope this helps.

it could be lifter tick (as eric pointed out), or an accessory pully issue. take a close listen to the engine bay at idle and determine where the noise is coming from. im pretty sure the noise is unrelated to the spark plug issue. you will KNOW when knock/piston slap/etc. is occuring.

you say i will know but i have no idea what it sounds like. the car runs fine, same as always. as for the source of the sound it sounds like its coming from the passenger side and its louder when i stick my head under the car. im kind of doubting knock/slap too because the noise doesnt get louder higher in the rpms, which i would think would happen with knock/slap...right? also, its quieter sometimes than others. dont know if any of this changes your opinions. thanks for the help

sounds like lifter tick to me. Don't sweat it. If it goes away at higher rpms, it is either because the engine is making more noise, or because it is finally getting all the oil it needs to feed the lifters.