Scheduled a quality assurance visit for a customer that we'd recently installed a new server room commercial HVAC for. System was working but customer wanted a humming noise checked. Tech inspected the new ICP air conditioner and found no unusual vibrations or parts out of place. Explained to the customer that the previous unit had been a direct drive system, and this new unit was belt driven, causing a slight increase in normal operating noise. Technician adjusted the motor speed slightly to bring down noise a little more. No other issues to report, job complete.