That depends on the level of sound and noise produced by other appliances in the room. For example, if there is a clothes dryer or central heating unit running in the same room as your bathroom fan, then it will probably reduce the audible volume of any whoosh sounds that come from your vent pipe. Similarly, some people find that if their hair dryer is nearby it helps to mask fan noise - but also tips them off when they need to replace their filter because pet hair has built up enough to block airflow.