HRVs are designed to be ultra quiet, when operating on normal speed. It is fair to describe the noise level as being difficult to hear, to a person with normal hearing, when the HRV is operating on normal ventilation speed.
In BOOST or maximum speed, (as when switched automatically by the hot water fan boost thermostat), the fans operate on high speed, and noise levels will increase. Those air outlets and inlets closest to the HRV may emit an audible noise, but usually this is not so loud as to be objectionable in a normal home. If this noise level is objectionable, use the speed controller to set the fan speed to a lower level, that is acceptable.
Other measures are practicable to control noise, that may be objectionable to persons with acute hearing…. a fibreglass blanket over the HRV will reduce all noise by at least 20%. Additional ducting, arranged with a 90° bend will reduce the noise level at the end of each duct.