I have been hearing this strange noise on 345.000 that sounds like a woodpecker/knocking sound. I first thought it was some local noise, but I'm picking this up from both San Diego and Riverside County (about 90 miles distance), so it must be something else. This freq is used by USCG aircraft --- could this be some type of signalling data mode?
Here is a record: http://cl.ly/MfI2/345.0000.mp3
Here is a record: http://cl.ly/MfI2/345.0000.mp3