The new complaint involves Western Digital calling 7200RPM drives "5400 RPM Class"—and the drives' own firmware report 5400 RPM via the SMART interface.
Recently, redditor /u/Amaroko placed a sample of that drive on an empty cardboard box, with a Blue Yeti mic held directly above it, then powered the drive on. Analysis of the recorded audio using Adobe Audition showed a baseline frequency of 120Hz for two models of WD 8TB "5400 RPM class" drive.
120 cycles/sec multiplied to 60 secs/min comes to 7,200 cycles/min. This means that "5400 RPM class" drives really were spinning at 7,200rpm.
While you might think that this means that you are getting a faster drive, there is a small problem of noise generation and power consumption. Users purchased drives which they expected to roll low and slow, but they got more noise, heat, and power consumption than they expected.
Western Digital has confirmed that "5400 RPM class" does not actually mean that a drive spins at 5,400rpm.
“For select products, Western Digital has published RPM speed within a “class” or “performance class” for numerous years rather than publishing specific spindle speeds. We also fine-tune select hard drive platforms and the related HDD characteristics to create several different variations of such platforms to meet different market or application needs”, the outfit said.