So I've found the file on my IBU2 SD card that's the song I heard (I wasn't going mad). It's labeled as plfull.wav. Now somehow I did something that made that song start playing out the tank and I have no idea how to reproduce it. Is it possible it was just a card error? Do the IBU2s sometimes just start playing random sound files that are on the SD card? Or is there some sequence on the handset that you can press that makes other sounds play? This is not the IBU2 pro btw, it's the standard.