Running a retrofit hydraulic roller cam

Sewing machine is smooth, this sound like a loose un pumped lifters.
Yup!
or the push rods haven't been clearanced,, contacting the cyl head..
IMO, probably not. I have had that problem and for me it was caught during assembly. While it was clearanced, after break in, running the engine a few thousand miles, some of the pushrods left witness marks as there clearance margin was low. No noise was auditable.