The central HVAC unit should make some amount of noise when running. This is necessary to keep the blades turning in the fan at a high speed.
If the central HVAC unit makes no noise, then that means that it does not have enough power for the fan pinion gear to wind up and push outwards against the unit blade holders.
A loud humming noise could mean loose wiring, while a rattling could indicate debris, and a hissing sound might require duct repair work. For any of these odd noises, it’s time to call in a professional.