It's interesting how a sound, music or image can make you relaxed almost instantly. To be honest I always had this affinity to the hair dryer noise, or white noise if you want to get more scientific. It just makes me relaxed, it's always like that when there's a fan. Especially recently, I recorded the sound of my fan heater and listen to it during the night on loop. It helps a lot sleeping and can also imagine the relaxing warmness from it.
So, what's your most relaxing soud, music or image?