Theres probably a vvti controller attached to the cam sprocket on each head. I know from previous experience of a failed vvti controller on another Toyota that it causes a separate fault code p1349 and causes the engine to judder at the vvti switching point as if it's going on/off the power repeatedly. Only in light throttle.
I think things like poor oil, lack of oil changes etc causes them to fail along with the chains but there are filters for the oil control valves that can get clogged giving vvti issues.
@ruutastic Ive heard of these engines sounding like a bag of bolts before. Certainly seen a few vids about it on the tube and I think the oil scavenge pump gets blamed.
I know mine taps away sometimes. Good luck getting it sussed.