I have spent lots of time listening and hearing odd signals.Here is a link of links that may be of help for identifying some of them.Hope it is useful.
http://www.freewebs.com/jimmzz91164/thoseweirdsounds.htm
Jim,N2NXZ
And here's quite a bit more on the subject - including software links to copy some of those wierd noises...
http://wiki.radioreference.com/index.php/HF_Digital_Decoding
73 Mike