93 maxima makes a strange tapping after spark plug change

[Green monster]

My 93 Maxima had a slight miss at idle. I changed out the spark plugs and found that the #6 plug was completely fouled. Now that I've changed the plugs, the #4 plug is missing and there's a new tapping sound to go with it. Has any one experienced this before? I could use some input before i start throwing parts at it. Any and all input will be appreciated

Thanx

Wendel

[maxhopper]

Check the gap on the plugs you installed. Try to narrow down where the tapping noise is coming from (injector, valve, etc).