Review on 🐠 Hygger Quiet Mini Small Aquarium Air Pump for Betta Fish Tank - Bubbler Oxygen Aerator with Air Stone, Tubing, and Suction Cup - Ideal for 0.5-15 Gallon Fish Bowls by Heather Bell

Apparently there's a new air pump technology that uses a vibrating piezoelectric element to move air. This pump had the same old 60Hz hum and associated familiar vibration, so clearly not piezoelectric. There was no air intake, so no air escaped from the exhaust; The block turned out to be 100% sealed around the entire perimeter. Although relatively quiet I cannot recommend this pump and it's coming back!