The following factors are to be considered to avoid affecting vibration/sound.

1. Avoid too much belt tension. There shall not be too much or too little belt tension, but a delicate balance shall be stricken between the two. If the belt tension is not enough, belt squeal will be caused. Too much belt tension will lead to vibrations. When adjustable motor pulleys are mounted on fans, sometimes the air-balancer may close the pulley and does not adjust the tension, which leads to too much belt tension.  

2. Upblast exhaust fans that are mounted with butterfly dampers can have “banging sounds”. In the warehouses that have dock doors face wind, the positive building pressure can cause the dampers to open to let the pressure through and then close after the pressure is relieved. The dampers can be held down by adding magnetic latches; the magnets can be overcome by the fan when powered on.  

3. Motor “hum” can be caused by speed controllers. There are only two types of single-phase motors that can be used with speed controllers. They are shaded pole and permanent split capacitor (PSC) motors. Except for those two, the other motors used with a speed controller will get burned. When the speed controller is adjusted down too far, it will get so inefficient and develop a hum. Also if the fan is restarted, it can have insufficient voltage to restart and trip the thermal overload.

4. Uneven air flow into a fan. When an elbow is too near the inlet of the fan, the air flowing into the fan may bring uneven load to the wheel, which leads to vibration.  

When you select a fan, look for the features that can save time in installation, beyond just picking the product of the lowest price. Talking about fan performance, keep in mind that the tests on fans were performed under the most theoretically ideal conditions. If the fan is installed in the way much different with the testing environment, it will not perform as catalogued. If an on-site problem occurs, you can refer to one of these installation tips that may save time and money and the issue may be resolved.