We've got a strange issue with interference. We've got 4 receivers stacked on top of one another. The top and bottom one seem to suffer some sort of interference indicated by one or two of the receiver lights going red whilst transmitter is switched off. It doesn't seem to be to do with the channels, if you swap the channels with the middle two that seem ok, it's still the top and bottom one that suffer.
Any thoughts - is it likely to be faulty units? Or related to RF1, RF2 modes (not sure which they are in - any way to tell?).