Black hawks are quiet enough for specops teams to use them in urban raids like the Bin Laden one.
The modifications probably required huge trade-offs in cost/performance and might still not be quiet enough for daily use in urban/residential areas.
Lilium boasts: "As well as a customized electric motor, it contains innovative liner technology which means the aircraft will be inaudible from the ground when flying above 400m and will only be as loud as a passing truck while taking off." https://lilium.com/the-jet