Not sure if this has already been said, since all replies doesn't load for some reason, but I have to recommend https://www.sigidwiki.com/wiki/Signal_Identification_Guide to everyone interested in SDR and radio stuff in general. I think it's somehow affiliated with https://www.rtl-sdr.com/ , it is at least linked from there, Anyway, there are a lot of different signals with spectrum views, audio samples and text about what they are. It was a great resource when I was playing with an RTL-SDR a while ago.