Ok, so here is what my process when researching noises -
Noise can be caused by mechanical components during their operation, and can also be related to pressure and liquid flow.
I identify every pump, motor, zone valve, blower etc. One by one I eliminate them.
2nd, I check pressure relief valves for signs of blow off, ant leaks in the system, and any sign of unit running a higher temp than desired.
Once in a great while something is found to simply be from design..
But in your case I would check circulating pumps, zones, and pressure relief.
One by one you can eliminate items.