UFOs shouldn't be synonymous with alien intelligence. If anything evolved to travel through the universe, wouldn't it be logical to assume that it originated from a place where this ability was necessary for survival, e.g. the edge of a black hole? Such a life form could be quite different from our rock-bound existence. They might be closer to fish than to us.
Stanisław Lem has explored this sort of idea in his works very often. Like in Solaris, where the entire planet is very clearly an organism - it exhibits reactions to events, it maybe even has conscious thought, but it's on such a gigantic scale and on such long timeline that any idea of "communicating" with it is just fantasy. Or in Fiasco where there is a whole planet covered in microorganisms which have evolved a "society" including weapons to defend themselves with, but which again have no way to communicate with us. Or in Invincible, where life has evolved into self assembling nano machines whose only directive is to survive and consume - clearly an "intelligent" construct but one which isn't in the slightest open to "communication". List of examples could go on and on and on.
