Hey all, For a couple months now, I've had this tap tap noise come and go. At first, I could swear it was a lifter, even lined up and started a motor swap. Halfway through the motor swap, at the point where everything was disconnected and the hoist was holding the motor up, I backed out 'cause the new motor wasn't what I thought it was. I put everything back together, and added some gaskets to the center and rear drivers side exhaust manifold ports. When I fired it back up and gave it some good hard driving, the sound was gone, and stayed away for a couple months. I had everything disconnected then reconnected, so I can't even pinpoint by what exactly I changed, just beefing up the exhaust seal. In the last month or so, it's come back with a vengeance. At first real spotty, here and there, and only in realllly hot conditions. In the last 3 weeks it's become full time. I added some motor honey, then some of that stuff they say is supposed to clean and quiet lifters, and now the sound is gone on first startup of the day, but comes back with every other startup or hard driving. Exhaust manifolds are super-tight, anymore and the bolt heads will come off... I tried listening to different parts of the motor with a tube to my ear, but can't seem to find it. I can't tell what part of the motor this sound is even coming from anymore. I would happily ignore it, but it's robbing power. Enough so that with the AC on, I have to floor it to keep pace up highway hills. Even with the AC off I have to give it too much juice to go. When the sound is not there, the truck feels like a stump puller (ok, maybe a little less, but feels like night and day with this noise). Any help is greatly appreciated!!!