I just replaced all 16 rocker/lifter assemblies in an 06, with genuine VM Motori parts. Now there's a rattle/buzz that I can't specifically recall being absent on this vehicle (one of five in the fleet I maintain), but quite certain is absent on the others. The engine's run a grand total of perhaps an hour since the replacement, most of it idling. The rig has a fuel delivery issue, waiting on parts to arrive, that's prevented a thorough warmup/shakedown drive. The noise occurs at low-mid RPM and may vary with load (further testing required to verify). I'm familiar with hydraulic lifter tick in general, and this doesn't sound lllike it, but I also observe that these lifters are half the size of any others I've seen, which would plausibly affect any acoustic signature.

Do our lifters sound like others, or significantly higher-pitched? Is the buzz/rattle in these circumstances commonly encountered and with an identifiable cause?

Purchase yourself a mechanics stethoscope and try to pinpoint the location of the noise.
You can find them online (Amazon) and at most automotive parts stores.

Hydraulic dampers & rocker arms should not make any noticeable noise as you described.
Could the noise be in the timing belt area?
Have you tried removing the serpentine belt and running the engine without it to see if the noise goes away? Rules out a lot of items!

_________________
Supporting Vendor and Moderator of LOST
05 Jeep Liberty CRD Limited
Ironman Springs/Bilstein/Shocks
Yeti StgIV Hot Tune
Week's BatteryTray
No FCV/EGR
Samcos/ProVent
SunCoast/Transgo
Carter Intank-pmp
2mic.Sec.Fuel Filter
Flowmaster/NO CAT
V6Airbox/noVH
GM11 Bld.fan/HDClutch
IronrockArms/wwdieselMount
98 Dodge Cummins 24 Valve