Well, I had this problem on my Charger. It has a 440 in it and recently starting popping through the carburetor. I thought the timing may have been off, then I checked the cap and rotor, which were new, replaced them with new spares I had anyway, still pops. The car would run great at idle, then as you give it gas it would start popping. So I thought since it had a Holley carb the power valve might have gone out on it. I replaced it with a REAL carburetor, a mint Carter AFB I borrowed from my dad's Cuda and I knew the carb worked damn good. It still popped. So last night, I took the valve covers off and couldn't have got more pissed off. 2 of the rocker adjusting nuts had come completely off. One on each head. It has Crane gold roller rockers and the nut you use to adjust the tension on the pushrod had come off and was laying in the head. I know for a fact I tightened them because you re-adjust your rockers after initial break in on the engine and I took my time doing it. Does anyone else know the nut I;m talking about? This has the shaft mounted rocker system and all these 2 nuts do is hold the adjustment in place. Thanks for any help and the info on the lifers. Now I'm pretty sure the noise I head was more than just the Rhoads at work. Is this a real serious matter for this engine to have a nut laying in the head while it's running? Doesn't sound like a good idea to me.