Hi,
You say it's an audible tick... it's highly likely that is coming from the relay(s), you could investigate by:
a) does it stop if you disconnect the relay(s) ?
b) add a delay(2000); in your program loop, does that make the tick stop for 2 seconds ?
This may indicate that your program is continuously pulsing the relay(s) when you don't think it should be.
You are correct that the usual one-diode-across-the-relay-coil won't work with a single-coil latching relay, but you can add several diodes like this:
The 4 diodes clamp the spikes from the coil switching
(ignore the LS244 part, I just googled for a sort-of suitable diagram from here )
Yours,
TonyWilk