An "Ear Rape" YTMND is one that is usually created solely for the purpose of annoying or causing pain to the viewer using loud and/or high pitched noises. The most common type of these sites use a square wave to create a high pitched whine and suffering.
Ear rape is generally done over ytmnd ventrilo, however it will earn you a ban (unless you are a senior user). There is quite a few popular sounds used for ear rape, generally because people are to lazy to make new ear rape sound clips. Blue noise is often used.
Some people use this as a method to troll on the YTMND vent, however this is generally ineffective due to moderators being on most of the time.