The Lt Daikin is one of the louder models (not sure from your post if you have the Lt or HT, the HT is supposedly one of the quieter models).  Having said that (and depending on your heating flow temp) dhw heating may well put more strain on the system than space heating.  I'm guessing that the showroom demo was doing a space heating cycle!

Could you try to find someone else who has one to compare, also on dhw cycle (maybe your installer could help).

Can you screen it somehow from the house or is there any way to isolate the compressor better without invalidating the warranty?

If the sales pitch was deceptive and you can somehow prove it, then perhaps you have a case for a claim.

I'd definitely lean hard on the installer given you specifically visited the showroom for a demo!

@jamespa Thanks. It's the Lt Monobloc. The water cylinder in the loft so the pump can't stray further from the house sadly. I wouldn't know how to isolate the compressor - I'm not an engineer and wouldn't dare to go in there.

The installer definitely didn't pitch it as a loud model. They're still waiting for Daikin's report but I'm not very hopeful at this stage as the Daikin technician was pretty clear on the noise being normal, nothing to repair

I am wondering how to prove my case here as the communication in the showroom was verbal, nothing in writing.

@sobo

As I think has already been pointed out, heat pumps are noisier when they are working harder (producing hotter water or during the defrost cycle).

Are there any hard surfaces, fences or brick walls around your heat pump?

How far is the back of the heat pump from your home wall?

You cannot put much in the way of sound proofing on the outside of the heat pump, without restricting the airflow through the unit, but it may be possible to absorb some of the sound on nearby surfaces.

As a test you could try collecting egg cartons and fixing them to a suitable board, which you could then position around the heat pump to try to absorb and lessen the sound.

You could also ask your installer if Daikin can provide any internal sound proofing around the compressor which is normally the main source of the sound.

Manufacturer's noise levels are usually quoted dB(A) SPL @ 1m free field. This means no reflective surfaces such as walls or floors. It's an unrealistic scenario, most ASHPs have at least 2 or 3 reflective surfaces. They increase the directivity of the noise - away from the source in the opposite direction to the reflective surface. If you're getting noise inside the house, I suspect noise and vibration is being transmitted into the structure of the property. For free-standing ASHPs, this is usually via the supply and return water pipes. Silly question time:

1) ASHP installed on rubber crumb or other vibration absorbing supports?

2) Not wall mounted on cantilever brackets?

3) Supply and return pipes have flexible sections which are not stressed & tight or clamped where they should have freedom of movement?

4) Pipes through the wall into the house have insulation sleeve, not touching block or brickwork? 

5) Compressor support is not distorted, and not touching or vibrating against the ASHP casing? 

As Derek & others point out, scheduled HW production is a high load on the compressor, it's working hard, pretty much flat out to raise hot water to 50+degC in a short time. Steady state house heating would see the compressor running at a lower frequency and power consumption, with less noise.

I'm not familiar with Daikin, but most compressors will have a moulded acoustic jacket around them, usually custom designed polystyrene or similar. They are very effective in reducing the compressor noise at source. Often the compressor is also in a separate enclosure from the coil & airflow section. Even with all that, the dominant noise of a monobloc is the compressor, sickle blade axial fans are whisper quiet.

My Grant Aerona 10kW has a stated dB(A) SPL @ 1m of 53. It's on the patio next to the back door with a glazed conservatory adjacent. Standard 28mm glazed units, PCVu panel back door. It's completely inaudible inside the house with windows and doors shut. The only noise evident in the house is some 'white noise' from the higher velocity in 28mm and 22mm heating pipework resulting from the ASHP retrofit. It's pumping over twice the volume flow the old boiler used to move around the same circuit.

Have you got a resonance or some other noise generation on the unit? The compressor operates through a wide range of frequencies, and the casing is very thin sheet metal. Sometimes you might get a rattle or a noise generated at a particular frequency the compressor is running at. Adding some gasket material, tweaking some fixings, or a cable tie or two can usually stop nuisance noises and rattles.

@derek-m
The pump is 40cm away from the house wall. The next nearest is the garden fence, ca 1.5 meters away.

@allyfish 
1) Crumb rubber feet.
2) No.
3) Beyond me - however the noise is from the unit not the pipe.
4) Yes, insulation sleeve between the pipes and wall.
5) Beyond me again, but the Daikin engineer opened it up and said all good. It doesn't sound like something is banging against the casing.

After going to listen to a other monoblocs, Vaillant and Midea, the difference is clear - other pumps sound like air blowing while mine sounds like a rattling machine, similar to a old supermarket fridge. I am surprised and concerned about Daikin's observation that this is normal.

@allyfish Our Daikin EDLA08E2V3 is an 8kW Monobloc version and sits some 33cm from the back wall (brick) of the house; it is mounted on 2 feet as will be seen in the attached photo. I cannot hear any particular sound from the compressor, in fact, all I have observed is the noise of the fan. This is during idle and heating mode alike, though DHW is handled by a Sunamp Thermino ePV210 unit and does not load the ASHP at any time. The unit was only installed in February but as a retired audio engineer, I am ver aware of irritating sounds / noise! Regards, Toodles

@toodles My pump is positioned similarly to yours, back to a wall and on two feet. I sincerely hope Daikin can fix the noise as my compressor is definitely very noisy.

@sobo attach some pictures if you can please? It's a new install under MCS, the white noise of the fan impeller plus a hum (not a rattle) of the compressor is typical. Noise is a subjective issue, and humans react differently to noise sensitivity and what we consider as acceptable. Seeing and comparing other installs of the same monobloc would let you determine if your unit is typical or not. If yours is louder than the same unit in a comparable installation, then you should take it further, perhaps with the MCS, or to get some calibrated sound level measurements made. Installed actual sound level will exceed catalogue data.

MCS020 allows, crudely, +3dB(A) per reflective surface, so a solid floor and wall to the rear could increase the noise measured at the front by up to 6dB(A).  Sound will reflect off the rear wall and floor and increase the sound pressure level at 1m from the front. 

Tootles' install above is ideal and best practise; gravel substrate for soak away of condensate, which is also non-reflective and absorptive surface, rubber crumb mounting feet.

My ASHP is straight onto pavers on a suspended beam and block patio with about a 4" sub-core and paving stone surface, rubber crumb feet but reflective floor and wall to rear.  Not as good as Toodles, but probably typical. To give some perspective, my neighbours oil fired boiler flue in his patio lean-to is considerably noisier than my ASHP running flat out. It's some 12 metres from my open office window now, but clearly audible when it fires up.

@Sobo, you could ask your installer to provide their complete MCS020 acoustic calculation estimate to you, if you don't already hold it. P.16 onwards refers.

MCSCERTIFIED.COM "https://mcscertified.com/wp-content/uploads/2021/10/MCS-020.pdf"

If you property is in relatively close proximity to neighbouring properties, MCS020 should have been completed as a means to determine permitted development compliance based on the estimated noise level at the nearest neighbouring property. If you live in glorious rural isolation, then your installer probably & reasonably didn't need to complete it. Note MCS020 clause 3.3; where MCS 020 is relevant, your installer is obliged to provide you with a copy of the completed assessment.

Subjective: if you do live in glorious rural isolation, your background noise level is likely to be very low. 40-45dB(A) is typical for urban and built up areas, but rural area background noise below 30dB(A) is common. This is where the perception of noise as nuisance comes in - the lower the general background noise, the noisier the ASHP will be perceived, and the more objectionable your perception of it be, even through the actual noise level is a constant.

Attached a photo of my heat pump. I couldn't upload an audio file here unfortunately.
I have heard two other Monobloc heat pumps in action: a Vaillant AroTherm and a Midea R32. Both produced a noise that could be described as air blow, whereas mine produces a rattle motor noise. The closest thing I could think of to describe it is a noisy fridge - closer in level to a big supermarket fridge than a home one.
I couldn't find anyone with a Daikin Monobloc to go and listen too unfortunately. However after listening to the Vaillant and Midea, I can say with confidence the difference is very explicit.

@sobo Sounds to me as though your heat pump has an abnormal noise if it rattles, as with mine and others, the fan noise equates to almost all the noise heard. Stick to your guns I say, I think you have a loose mounting or similar if you can hear a rattle. Regards, Toodles.