Sounds like a gremlin
An imaginary mischievous sprite regarded as responsible for an unexplained problem or fault, especially a mechanical or electronic one: a gremlin in my computer omitted a line
Oxford Dictionaries Online
For a longer discussion, see this article in Wikipedia
Also, there is a wonderful dramatization of the gremlin effect in aviation in Nightmare at 20,00 Feet, a Twilight Zone episode with William Shatner (Galloping around the cosmos is a game for the young. - Captain Kirk).