Noisy portable air conditioner at night, how to reduce the decibels?

I ended up dealing with this problem during a road trip last summer - I was in a rental apartment in Tuscany with one of these portable air conditioners that made a terrible noise at night. I couldn't sleep, it was frustrating after 8 hours of driving. I discovered some tricks that really work. The most important thing is soundproofing: put the air conditioner as far away from the bed as possible, maybe behind a piece of furniture or behind a heavy curtain. If you can, create a barrier with towels or foam panels around the part that vibrates. The external discharge tube also adds noise, so make sure it's well secured and doesn't bang against anything. If the tube goes out the window, seal it well around the edges with insulating tape so it doesn't have spaces where it can vibrate.

Another thing I tried is putting the air conditioner on a soft surface - I used a thick rug or even bath slippers under the feet to dampen the vibrations. Sounds weird but it really works. Also check if it's set to minimum speed: often when you lower the power the noise drops significantly. If you really can't manage it, consider that many newer models have a night mode that reduces the fan speed automatically. It's worth checking in the manual if yours has this feature. In my case I solved it mostly by putting it in the next room and leaving the doors open - the air flow still reached where I needed it without hearing the constant rumbling.