Update - resolved - see this post.

I have a small Daikin Cora FTXM25U high wall heat pump in my office. It's a few years old, and the whole time I've had it the indoor unit occasionally makes an incredibly annoying ticking / clicking type noise. Some days it doesn't do it at all, some days it does it for half an hour. The noise sounds like it's coming from about 5cm from the left hand side, centered vertically and horizontally, behind the metal heat exchanger. As the fan speeds up and slows down the ticking noise gets faster and slower, and if it's making the noise when it finishes the heating cycle I can hear it getting slower and slower until the motor stops. It's a little like a piece of plastic on a bicycle forks hitting the wheel spokes.

Pushing up on the bottom of the plastic housing on the left hand side stops the noise while I hold it, but it comes back either immediately after it drops back down or a minute later. Nothing else seems to reduce the noise. I don't have the swing functions enabled, they make no different anyway - I checked.

I've had the installer, an electrician, out three times to try to fix it. The first time they loosened some screws where it attaches to the wall which reduced it a bit. The second time they couldn't reproduce and did nothing. The third time they couldn't reproduce, they took the plastic case off but they put a few packers between the unit and the wall, and it seems to be a little worse since then. It's annoying enough that I sometimes end up turning the whole thing off and getting cold. They've apparently talked to Daikin about it and they didn't have any suggestions.

The noise most often happens later when the unit is almost up to heat and isn't working that hard. If often happens if I go back into the office and turn the heating on later afternoon or in the evening.

I've uploaded a recording to SoundCloud here.

Any suggestions? I don't see a lot of point getting the electrician back without a few ideas or suggestions how to reproduce it. The electrician firm who installed it does lots of things including HVAC but that means they're less experienced with this than someone who does it all day every day.