Avoid cable sounds made by vibrations or knocks on your in-ear headphones.

Usually the term microphonics is misused to describe the mechanical
vibrations or knocks that travel to the ear physically via the cable of the headphones. 
(See wikipedia for more info)

Anyway those sounds can really annoy the users of in-ear headphones, so how can we solve that problem?
There are some clever ways to deal with vibrations:
You can and should if possible make the cable of your in-ear go over your
ear, this way the vibrations will be absorbed before they arrived to the ear canal.
The use of a cable clip also kills some of those nasty sounds.
Making a cable sleeve to dissipate vibrations.

The best way to avoid those sounds is to prevent the cable from moving
around, so keep it organized by using those tips and you should be almost
free from vibration sounds.

Note: Using the cable over the ear might look strange but Shure also uses
it to avoid vibrations on their expensive in-ear monitors.