i have a 69 chevelle SS with a 396 & M22 4speed. it has been rebuilt with a mild summit cam, a mallory HEI, and CR has been brought down to 9.5:1, everything else is stock. the car isnt run much but runs good until tonight(i pamper it). i just now took it out for a drive, when in second gear at about 3500rpm it suddenly started making a popping sound. i have never heard a sound like this before. the best description is 'pop, pop, pop, pop...' but very rapid. it does this in first(3000rpm), second(35000rpm), third(3500rpm) but does NOT in fourth no matter what rpm i floor it at. any help would be much appreciated. Knife.