Im having a tough time figuring this one out. When im at WOT on the freeway i get this random pop between 4k and 6k rpm. its kinda fiant but its noticeable. i pulled 4 of my plugs(2 from each side), and found that they were in perfect condition. im using 91 octane from 76, my Predator tuner set at 20% increase in timing, and ive got 106k on the motor. any thoughts???