Well I've got an Ecodan. The heat pump outside is really quiet, but even so I can't even hear any internal pumps in action.

We have an 11.2kW Ecodan.  I noticed that the compressor was notably louder at lower ambient temperatures, eg approaching and below 0degC, due to the compressor being required to work harder.  

I made some enquiries about the "Quiet Mode" option in the controller.  Apparently on Ecodans it simply limits the compressor speed to reduce maximum noise output. Obviously this also reduces the maximum capacity of the heat pump.

As our heat pump has been conservatively sized, I decided to trial the unit set to full time Quiet Mode.  So far it has operated fine when set on the quietest option, including when we had sub-zero temps for a few days in January.  The unit is noticeably quieter now too.

Posted by: @skd

We have an 11.2kW Ecodan.  I noticed that the compressor was notably louder at lower ambient temperatures, eg approaching and below 0degC, due to the compressor being required to work harder.  

I made some enquiries about the "Quiet Mode" option in the controller.  Apparently on Ecodans it simply limits the compressor speed to reduce maximum noise output. Obviously this also reduces the maximum capacity of the heat pump.

As our heat pump has been conservatively sized, I decided to trial the unit set to full time Quiet Mode.  So far it has operated fine when set on the quietest option, including when we had sub-zero temps for a few days in January.  The unit is noticeably quieter now too.

Just to add, our DHW cylinder is also Ecodan.  The three pumps were supplied by Mitsubishi as part of the pre-plumbed package.  They all have a slight hum when operating but none are intrusive...even with the radiator circuit pump set to max flow.

@skd @SuzeR

We also have an 11.2kW Ecodan.  Generally very quiet except when the ambient drops.  We only have one internal pump (something I am still trying to get rectified by our installer) and it does make quite a bit more noise than I would like, although I have also learned to sleep through it!

I wish we had had the opportunity to have the pre-plumbed Ecodan cylinder installed, but I don't think it would have fitted into our airing cupboard.

All decent heat pumps are variable speed, the outdoor units are quiet on warm days and noisiest when it's cold and wet. Indoors they should be pretty much silent.

The water pumps are very quiet when running. If you can heat them either there is air mixed in the water, you will hear noises like a tap running. It's super hard to get the air out. I would install a spirotech deaerator if you have this issue.

If you have water flowing noise in your radiators your system needs balancing. Balancing is easy but rarely done anymore. It's very important with high water speed heating like heat pumps. 

Sounds like you need to call the installer back for a mid season tweak. 

Good luck. 

It is a very loud humming noise, which is louder when water is heating. No radiator s, all underfloor heating.

that is not good, you need the installer back. i have 4 pumps on my heat pump all in the same cupboard, i cant heat mine, there is something wrong with your system.