The Sound Dilemma (unproduced TV story)

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The Sound Dilemma was a story of Doctor Who: The Animated Series featuring the Eighth Doctor. (VV 5)

Plot Summary
Yes, there was a beryllium chip installed in the TARDIS, but not for the reasons you may think. And now that chip has died out and its outflux of radiation is turning the TARDIS quite mad. The Doctor and Liz are separated by a jealous TARDIS and Liz faces a deadly monster in a pit while the Doctor faces a cunning TARDIS made duplicate of himself which wants to erase him and then become him. And it will kill him to do it... (VV 5)