Leaderboard

My rig would occasionally make that exact sound on start up. When I replaced the head gaskets, I found one lifter had a cleaved face on it, so I replaced it. Since then, the sound has not recurred. My bet, if you tear it down to the valve covers, you'll find a smoking gun there with the noise. A bad rod bearing is more of a knock As far as backfiring, it would make sense to me that you probably have an injector issue. I had a slight misfire for the longest time, mostly audible at the tailpipe more than anywhere else. Eventually, the culprits outright failed. After replacing the failed injectors, the misfire completely went away and some amount of power was gained in the process. If you can identify a possible single failed/failing injector, the perfect time to replace it would be when the upper intake is off.