I'll never forget when I was about 11 and my mom and two brothers and I travelled out West. We'd just crossed from Arizona into California when we heard this "whoop, whoop" noise and saw a huge red ball glowing in the sky in front of us! Sent a chill down our spines until we realized it was the sun (it's alot bigger in the sky out West) and a (then) new ambulance siren..
I don't discount the possibility of UFO's tho.. of course once we know what they are, they'll be IFO's..

Ark! We come in peace!