I have a C8 with MK Flight control. Sometimes during flight I receive a low frequency beep in the earphones connected to the controller. MX20 I have audio/vario enabled and receive the ascent/decent tones but this is much lower and a single lower tone. It just occurs now and then (seems to be in level flight). It doesn't seem to be related to an error or function. Can anyone explain to me what this might be?
It is possible that the transmitter is indicating loss of contact with the receiver -- this could be a function of Tx to Rx distance or shadowing of the Rx antennae by the carbon fiber. You could perhaps simulate this by briefly turning off the Rx and seeing what noises the Tx makes. Also, if you download the voice file for the MX20 and place it on the SD card, you could turn on MK specific spoken audio responses. Andy.