Most people are unaware that there is slight but detectable vibration in the personal computer. Originally the PSU fan was the only contributor. Later the CPU needed a fan as the power consumption grew. Finally chassis fans were added to help remove waste heat from machines which added even more vibration.
Hard disks are prescission make devices. When several are stacked in a server the movement of the read/write heads adds to the overall vibration.
Vibration is usually measured compared to the force of gravity. 1G = 9.8 m/s² which calibrated to sea level. Vibration is also considers the frequency of the vibration. A typical PC has a vibration frequency range of 5-2000 Hz.
A high-end hard disk may be able to handle a maximum of 0.75G at a frequency of 5-300 Hz while in operation. Disks can be jarred when an adjacent server is removed for replacement etc.
A head crash occurs when the read/write assemble abrades the disk surface so designs consider ways to reduce the chance that will be an issue. A head crash can result in a hard disk failure. More concerning with excessive vibration is the heads on a disk are unable to settle properly on the right track. This can impact the performance.
PC chassis disk trays now have rubber grommets which can reduce vibration slightly. Rubber grommets are low cost which is why even the lower cost chassis models are equipped with them. Gromets are mass produced and are widely used with chassis fans and they can be used in many places to ensure the system noise is minimized.