On Monday, November 12, 2018 at 11:50:19 AM UTC-5, Adrian Tuddenham wrote:
I have two Tascam DR-05 recorders and they both exhibit the same
phenomenon: when they are recording complete silence, there are faint
irregular ticking noises on the left channel.

This occurs when using an external circuit which disconnects the
internal mics, but the circuit only needs to be plugged in, not
connected to anything, for it to happen. If there is any sound on the
channel, the noise immediately stops, but re-starts about one second
after complete silence returns.

To be clear, this doesn't happen when using the internal mics?

What sort of "external circuit" are we talking about?

If it only happens when recording silence, wouldn't that be easily mitigated with post production software?

But if it's a design problem, I would try adding an osc signal above audible frequencies at low levels right at the input jack. Should have no effect on the recorded audio and may be enough to keep the phenomenon from happening. If there's no room inside the Tascam, maybe you can add it to the external circuit.