2 Questions the one I'm worried about is the popping noise in my exhaust...

Ok, I have a popping noise in my exhaust. Only does it at idle. It doesn't do it while I'm in gear, or atleast I don't hear it. Recent mods to my car if you haven't seen my recent post was sparkplugs, sparkplug wires, new dist cap, and rotor. I figured it might stop after putting new plugs in it, but no luck. Any clues to what could be causing this popping noise?

Second question is: Whats the difference between a bigger mm wire. Like whats the difference from the 7mm to 10mm wire performance wise. If I get a bigger mm wire do I have to get different sparkplugs or would the gap just change? Sorry its a newbie question, but I'm a newbie : ).