Hi Alex I put the unit out for a couple of nights using the 5V usb - the same SD card - but I think the results are worse. There is a very audible beat. The bottom axis is seconds. Regards Ian

HI Alex Thank you for getting back to me. You can hear the click when you reduce the speed (so that you can 'hear' bats). The batteries are Energizer NiMh fully charged (4.2V) and the card is a Sandisk 32G Ultra. The batteries lasted for over 4 nights, in fact they lasted longer than the card capacity. Can you connect a 5V USB supply? If so what switch setting do you use? Regards Ian

I have noticed that there is a 'clicking' and occasional 'buz' at around 18KHz - 24KHz on all of my recordings. Recording set to 48K, 24bit and this is a snip. Regards Ian