Any idea what is causing this? I was having issues with the spark plug threads but finally got my new NGK CR7HSA spark plug fully seated but it still did this. Actually, it did this to 3 plugs in all. Not sure if it could have anything to do with the thread issues(unlikely I'd think). Prior to this it was sounding like it was about to start but just maybe not enough spark. Any help would be appreciated. Thanks so much!