Phenomenon that causes music to sound like it's being played at a different tempo than remembered? Something I've noticed now and then is that I'll be listening to a song off my music player and it sounds like it's being played in a tempo faster or slower than I remember the song being. Is this a defined/known phenomenon, and if so what is it's name and cause/reason for happening?
Vitouch et. al (2006) observed that "visual tempo significantly influenced 
the retrieved music tempo.".


  Music is known to potentially affect the perception of visual  scenes
  (e. g., Vitouch, 2001), as proficiently demonstrated  in the movies.
  But do films also influence the perception of  music? This study
  investigates cross-modal influences in  perception, taking influences
  of “visual tempo” on  perceived/retrieved music tempo as a model.


They conclude:


  Both studies demonstrate clear crossover effects: There is  not just
  “musical driving” of film scenes, but also “visual  driving” of music
  perception. Results hint to holistic memory representations of
  audio-visual material.




On the other hand, an older paper by Levitin and Cook (1996) observes that long term memory for music can preserve the absolute tempo, even by non-trained musicians. They do not investigate the influence of visual stimuli as in the previous paper.


  We report evidence that long term memory retains  absolute (accurate)
  features of perceptual events. Specifically, we  show that memory for
  music seems to preserve the absolute tempo  of the musical
  performance. In Experiment 1, 46 subjects sang  popular songs from
  memory, and their tempos were compared to  recorded versions of the
  songs. Seventy-two of the subjects came within  8% of the actual tempo
  on two consecutive trials (using different  songs), demonstrating
  accuracy near the perceptual threshold (JND)  for tempo. In Experiment
  2, a control experiment, we found that  folk songs lacking a tempo
  standard generally have a large variability in tempo; this counters
  arguments that memory for the  tempo of remembered songs is driven by
  articulatory constraints.  The relevance of the current findings to
  theories of perceptual  memory and memory for music are discussed.



Oliver Vitouch, Sandra Sovdat, Norman Höller (2006) Audio-vision: Visual input drives perceived music tempo. 9th International Conference on Music Perception and Cognition
Levitin, D. J. &amp; Cook, Perry R.(1996) Memory for musical tempo: Additional evidence that auditory memory is absolute. Perception &amp; Psychophysics, 58, pp. 927-935.