Comment 2 for bug 140924

What does that do?

According to the manual:

 -M Get/set Automatic Acoustic Management (AAM)
  setting. Most modern harddisk drives have the ability
  to speed down the head movements to reduce their noise
  output. The possible values are between 0 and 254. 128
  is the most quiet (and therefore slowest) setting and
  254 the fastest (and loudest). Some drives have only
  two levels (quiet / fast), while others may have
  different levels between 128 and 254. At the moment,
  most drives only support 3 options, off, quiet, and
  fast. These have been assigned the values 0, 128, and
  254 at present, respectively, but integer space has
  been incorporated for future expansion, should this
  change.

the only valid numbers are 0, 128, and 254. 254 is the loudest.