Hydraulic lifters from my understanding are known to do that if they sit for days for sure, my 07 Tundra with the 5.7 will make a raquet when it has sat for a long time, i took it to toyota under warranty and they explained the hydraulic lifter thing to me, talked to several mechanics that said the same. Tundra has 312k miles on it, burns no oil, runs like new still....but only makes the lifter noise if it sits for days..when i mean days i mean about 4 or 5. Hope you get this figured out. Maybe its something simple like the others are suggesting.
