Sound fluctuates while playing audio and video files

I have been playing vob files , xvids etc and mp3 files on the wdtv media player. The quality is great on all but we have noticed that when there is a change of tone or depth of volume on files themselves the volume seems to go up and down to compensate for this.  If a track starts quietly for instance and then gets more powerful quite quickly the media player almost seems to want to lower the volume itself. Difficult to explain but hope you get what I mean.

This happens on films as well, if there is a sudden burst of loudness the machine seems to want to acclimatise itself to it which is quite annoying and distracting.

Any ideas, advice appreciated.

Jim

In answer to my own question. I went into sound settings on my Sony Bravia TV and changed highlighted TV speakers to external speakers and also changed the setting that said  originally A instead to stereo. Played a track that I had trouble with before and it played perfectly ,no fluctuation.

 I bought some Creative labs t20 speakers to go with the Bravia and wd hdtv  after reading many good reviews about them. They are fantastic giving very good sound and are quite small. They connect via the headphone jack if needed.