Any way to soundproof outdoor unit?

I've been using my new PortaSplit for the past month, and I'm very happy with it. I live on the top floor of my building, with the outdoor unit placed on the floor of my balcony. It isn't visible from outside the building, but I'm concerned that my neighbours below might be able to hear it.

The area where I live is exceptionally quiet—there is virtually no background noise other than birds singing. Because of that, I'm worried that the outdoor unit could be noticeable.

I'd also prefer that no one knows I have this unit. As I understand it, it's something of a gray area in Switzerland. Although it's marketed as a portable air conditioner, it does have an outdoor unit, and in my canton, air conditioners generally aren't permitted without going through a lengthy approval process or obtaining authorization.

The unit itself doesn't vibrate, so vibration pads wouldn't make any difference. My concern is the humming noise from the outdoor unit, which I find quite noticeable, especially in such a quiet environment.

I know the PortaSplit has an "Outdoor Silent Mode," but it also forces the indoor unit's fan to run at its lowest speed. I'd rather not use that, as I prefer to keep the indoor fan running faster for better air circulation and cooling.

I'm hoping there is a way to reduce or muffle the humming noise from the outdoor unit itself without using Silent Mode, restricting airflow, or risking the unit overheating.

I was wondering whether there are any specially designed acoustic covers or noise-reduction enclosures for outdoor units that could help reduce the humming noise while still allowing sufficient airflow and ventilation.

Has anyone found a safe and effective solution for reducing this type of noise?