Neither aliens nor alien spacecraft are known and proven to exist. In that sense, the answer is no. UFO means "unidentified flying object", not "alien spacecraft".
If there are aliens out there on other planets, and they see something they themselves cannot identify up in the air, then in that sense there is an alien UFO.
No.
UFOs are simply things that not readily identified. They are not 'alien' spaceships. Nor do they defy gravity and there are many phenomena that do not make any noise.
using UFOS
Chasing UFOs - 2012 Alien Cowboys 1-3 was released on: USA: 6 July 2012
Alien Paranormal Bigfoot UFOs and the Men in Black - 2013 was released on: USA: 1 June 2013
Chasing UFOs - 2012 Alien Castaways 1-7 was released on: USA: 10 August 2012
There is no confirmed evidence in favour of this.
No. UFOs are proof that some people have seen things in the sky that they themselves cannot identify. That is what UFO means, not *alien spacecraft*. There has never been the slightest shred of evidence that *any* UFO was an alien spacecraft, so the answer to your question is no.
Chasing UFOs - 2012 Alien Baby Farm 1-8 was released on: USA: 17 August 2012
Unsealed Alien Files - 2012 II Soviet UFOs 2-5 was released on: USA: 30 September 2013
Unsealed Alien Files - 2012 II Nazis and UFOs 1-10 was released on: USA: 24 November 2012
There is no reason to think UFOs are alien spacecraft, or that anything is "living in them". They're just things people see that they themselves can't identify-- that is what the U in UFO stands for, "unidentified". If they were alien spacecraft we would call them IAS, "Identified Alien Spacecraft". If you believe it then aliens.