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This may not be what you want to hear, but this is completely normal for the truck. Most of the newer motors use HLA's (hydraulic lash adjusters, or lifters) which tend to be louder than the older style buckets where you periodically have to re-shim them and adjust the valve lash manually. Your truck also has VVT-i which those actuators also make a bit of noise, particularly at idle.
If you compare it side by side to a half dozen other identical tacomas, you'll find some quieter, and some louder. They all do it, some worse than others. It's just the design of the engine. There are some bulletins out for some of the other motors that worry people, talking about the ticking noise or a rattle noise, particularly on a cold start. They all do it, but even then the ones that the bulletins refer to is VERY noticeable, like wake the dead kind of rattle. IT sounds like the engine is coming apart (Even though it's not).
Really the best thing you can do is visit your dealer and have one of the more experienced techs listen to it. There is a very, very small chance of a collapsed HLA, though I really haven't seen many of these. 99.9% of the time it is completely normal.