Hi Den and Julie,
The water lines through the fridge do vibrate a bit, so if they come in contact with a panel on the boat that resonates then you can hear it. However, in your case it's intermittent, so I wonder if there is some debris in your lines which is causing partial blockage and causing the lines to vibrate more.
it might be time to flush the lines with something. I do mine with white vinegar, letting it lie for 24 hours before flushing through. To be honest I don't have any clear evidence that it works, other than the fact my lines keep working ok!
Other owners use stronger solutions, Barnacle Buster is a product that some folks swear by. I guess it depends on what you can get in Croatia.
Cheers
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Dean Gillies
SV Stella *****, Amel 54-154
