Two new AudioMoths arrived on Friday HOORAY ! I noticed that one of them seems to put a pulse in the recording, apparently with harmonics. See attached pic.
Recordings from both machines enclosed together in a heavily padded box hopefully excluding any exterior sounds ! The right pic (suffix AM4) shows the odd pulse which appears to occur randomly but quiet frequently, perhaps 10 or 15 minute intervals. The left pic (suffixAM3) has not shown this at all so far. For info', one of my old units also showed this on occasions but then only every several hours or days apart !