If a contractor is being paid a fixed price to perform an installation they are incentivised to use the shortest cable run either to reduce time or material costs. An installation quote that includes the cable run length should remove that as a problem.
Removing the retailer as an intermediary and buying the heat pump from the installers should be much cheaper. There are big differences between what different retailers charge too.
These pages explain the difference between sound power and pressure levels.
http://www.sengpielaudio.com/calculator-soundpower.htm
http://www.sengpielaudio.com/calculator-soundlevel.htm