Hydraulic should only make noise (caused by the roller leaving the lobe and landing again) when the spring pressure + lift rate exceed the hydraulic pressure in the tappet, and the plunger compresses. The lifter's leak rate may be too high, oil supply volume in the gallery too small, or viscosity or oil pressure too low.
Am I missing something?

Some beehive failures are from using a light spring believing that the design simply replaces a heavier cylindrical spring.
The design saves some reciprocating weight (less wire mass, smaller retainer) but the advantage is multiple progressive rate (instead of linear) - but if harmonic float isn't a problem you may not have enough pressure.