Tuning back and forth over a small frequency range on 18Mhz all signals appear and disappear. I can hear a relay click as this happens. I suspect the autotuner. I am not transmitting, just receiving. The SWR over this range is about 3 to 1 and does not change much. See video
I wonder if this is a LOW Pass filter clicking in??? I have a Icom R-8600 that acts this way at certain frequencies.. Not sure if the 6400 lets you switch them off or not???? Flex will know the answer.