Excessive vibration shortens bearing life, loosens fasteners and can crack welds, so it should never be ignored. The most common cause is impeller imbalance, often from dust buildup or uneven wear on the blades. Other frequent causes are shaft or coupling misalignment, loose mounting bolts, worn bearings and a resonant base structure. Each leaves a characteristic signature in a vibration spectrum.
The practical fix sequence is: clean the impeller and re-check balance, verify alignment and tighten the base, then inspect bearings and the drive. Fans that were balanced to G6.3 and run-tested at the factory start from a known-good baseline, which makes on-site diagnosis far easier. Where an impeller is worn past cleaning, a balanced replacement restores the fan to its tested condition.