I have a ford explorer and it makes a noise like a police siren from the rear very occasionally,?

does anyone know what it is? And no, it isnt a copper behind me!
Answers:
Your Alarm Siren Is At The Back Bottom Of The Car And Is Shorting.
wow, make the most of it and arrest someone
its a FORD..
check your exhaust pipe, a prankster could have puit a exhaust whistle up it, i've used em many times. lol
i dunno, but i would use that to an advantage, try pulling a few people over
Somebody put a whistler gag in your tailpipe.
My father has an '03 Explorer and has had several nagging issues with it as well (AC problems, making weird noises, etc.). My best advice is to just take it to the repair shop for a full analysis and have the problems fixed by their service department. Better yet, get rid of it if you can.
You have a Whistle Tip! You Rock the House. Check this out:

http://youtube.com/watch?v=nnzw_i4ymkk.
Boy I hope its not an explorer 2002 or older..if it is, get rid of it..thats a death trap! If you are driving an older one around, thats a warning siren trying to say to you "GET RID OF ME!" They rollover because the center of gravity is too high on the older ones..and NO, its not the dang tires..do the research! If its a newer model, I dont know what it is other than a warning that you should get it checked out!!
Not trying to scare you..just want you to know what the older models are like..Ford FINALLY improved its explorers after 2002. So if you do have an older model..please consider getting rid of it!
(((personal experience)))
Sound to me like your rear end differential is dry and needs grease. Could also be premature wear on the same caused by lack of lubrication