I used to live close to a military air base and at night (not every night, but when I did hear it, it was always around 2-3am) I would hear these sounds. They would last about 15-20 minutes and I can only described them as 'Close Encounter' sounds... you know like the 'communication tones' they have in the film? The first night I didn't think much of it, as I thought I had just had one of those 'you dream you are awake, but you're not'-dreams. But then I heard it more often. It really freaked me out as I lived on my own at the time and I really started to doubt my own sanity as far as that I really started to think it might be UFOs, because I could ONLY hear the tones, but no 'air plane engine' sound to go with it. I told my boyfriend (now husband) about it, and when he spend the night we agreed I would wake him up if I heard it again. I am sure he thought that when he heard it he would be able to reassure me easily and explain what it was... but, when I did wake him up, even he seemed a bit freaked, although I could tell he was trying not to let on. So... we got up and got dressed and went outside to see where it was coming from (I hadn't had the courage to do anything more than look out of my bedroom window before). We walked around for quite some time, and both agreed the sound was coming from the sky, but he also couldn't hear engine noises... The noise went away almost as soon as we started walking around outside (which was odd as it normally lasted much longer on other nights, so I was a bit disappointed as it kept us from finding where the sound came from) after about 10-15 minutes we decided to go back home and to bed. It crossed my mind that one of my neighbours could be pranking... but realistically the sounds were too loud and clear (i.e. not muffled by walls, unless they had a huge open window or where outside themselves) for it, and my partner also agreed the sounds seemed to be coming from the sky rather than a nearby building. The airbase I lived close to is Volkel Airbase. This is a Dutch airbase, BUT it has Americans stationed there to look after the nukes. (This is not publicly admitted to by the government but common knowledge among locals AND former Dutch Prime Minister Ruud Lubbers recently publicly admitted to this - possibly by accident).I also know they have/had AWACS there. So in the end we decided that it must have been the AWACS radar making the sound when it's flying at night. (don't know how it can 'hover' over the same 2-block area that long though) Still, after all this time I am not 100% convinced this is true though. Is it? Does an AWACS make 'close encounter' tone noises when engaging it's radar at night? Or maybe even another 'silent' military airplane we haven't heard about yet? BTW, I do know what an owl sounds like, and a fox or whatever... but this was definitely not an 'natural' sound. If you would have said my neighbour was playing his keyboard very loudly in the middle of night you would be closer... (but not quite). You might also want to know that there were no high rise buildings for miles, but there are some electricity pylons only about 500 yards away...All this happened at the end of 2001/beginning of 2002 (I heard it on at least 3 separate occasions, probably more but I know it was at least twice before I mentioned it to my boyfriend.) I have been trying to find out what it was off and on ever since. Since 2010-11 more weird sounds seem to have been heard by people around the world, but going through the videos on YouTube, none of them really seem to hit the mark, as most of those seem to be a hum or metallic sound.I thought that if it was military experimental planes I would have heard about it by now, but... nothing so far. But maybe you might know something that the general public don't know yet. If so, I'd love to hear your take on this.Thanks very much in advance,Wendy-Anne Appleby