I've been dismantling an old hard disk drive (as you do) and it has a mystery bath-shaped component which sits loosely in a hole in the drive chassis and was held in place only by a sticky label. It's about 20mm x 5mm x 4mm and has a clear plastic housing containing a few hundred non-magnetic uniform black spheres each about 0.8mm diameter. Just below the bath lid there are two sinuous elements which look like electrodes, although there are no external connections to these. There are minute holes at the inner ends of these elements, suggesting vias. Any ideas as to the function of this component?

 

WAG Looks like an air filter. The convolutions are possible dust traps. The balls are silica moisture absorbents.

 

They have an air filter, with the air being stirred round by the motion of the disk.
https://www.datarecoverytools.co.uk...-circulation-and-air-filtration-of-hard-disk/

 

Thanks guys. I guess the serpentine nature of the 'electrodes' throttles the air flow.