Stop what you're doing for just a minute and listen to all the sounds around you. Even if you're reading this from home with no television or music in the background, you probably still hear the hum of a refrigerator, your computer's fan, or air blowing from your air conditioner or heater. You probably hear SOMETHING. Now imagine for a minute that you hear that sound 24 hours a day, 7 days a week.
Think about the sounds your fish experience all day everyday, such as the vibration of the filter, especially if it's a HOB filter or an external canister filter. If you have an airstone, imagine the constant sound of the bubbles. If you have a powerhead, imagine the constant hum of the pump. In a closed environment, resonance is typically greater than in open space due to sound wave reverberation.
Freshwater biotopes from which many cichlids originate aren't devoid of sound, e.g., waves crashing on shore in Lake Malawi, the current moving through rocks, surface noise from winds. There are lots of natural sounds in freshwater environments. However, most cichlids in the hobby aren't wild caught. They're domestically bred in closed systems, typically tanks or small ponds. Thus, anthropogenic (man made) sounds are ubiquitous. They're also controllable. Aquarium housed fish typically endure enough stressors without needlessly adding more. Yes, fish can be adversely affected by noise, including damage to their ears. Thus, it's not a bad idea to be cognizant of how you might be impacting your fish by the choices you make for their environment.
The Cichlid Room Companion
Tropical Fish Hobbyist
American Cichlid Assoc.
African Cichlid Hub