Sound Rating On Heat Pumps

[HTSEngineering]

I was wondering if anyone knows who sets the standards for sound levels in a heat pump, I believe in Canada its the CSA but there isn't much information available. If anyone knows the help would be greatly appreciated. The heat pump I'm looking at now is at 51 dba in the office it is cooling and the customer is complaining. Right at the heat pump the sound rating is 62 dba.

Thanks

[desA]

Where does the noise originate from?

[HTSEngineering]

Compressor and fan but the compressor already has a sound blanket around it.

[Brian_UK]

Any pipes vibrating or touching the casing?

[Magoo]

Generally units are rated on "open feild at x metres ", as in middle of a paddock. So if outdoor unit is in an alley way for example, the noise reverbirates around until it can escape upwards. Imagine a lazer light in a shiny enviroment, the sound waves act the same. So if the problem is the out door unit, instal a wall at 'x 'metres in front made of soft / floppy spongy rubber or similar, that will soak up pulse of sound waves.
magoo