There's no outside noise in a ground-source system (for all practical values of noise: it's just flow in insulated pipes). The pumps are nearly inaudible inside the mechanical room as well.

Inverter-based air-source outdoor units are nearly inaudible during any time when your neighbors are likely to have their windows open. When the weather is uncomfortable enough to have the units need to run at high-speeds, they are no longer inaudible, but the neighbors are likely to have their windows closed.

I'm looking at a system now that is 45 decibels - 10db quieter than my robovacuum which is one of the quietest in the market.