I am convinced that the reason why quiet household sounds are relaxing is exactly BECAUSE they have no rhythm.
We hear music all day long. At home, in the car, in the mall, in each store, in the restaurant, practically 24/7. I don’t listen to music in my car and I will drive miles further to avoid a gas station that plays music. I detest restaurants that play loud music and malls are only for emergencies.
Being surrounded by different kinds of rhythm all day long it has to be the very quality of no-rhythm that makes ASMR so appealing.
The thing to do then, is to treat sounds as if they are ocean waves playing in the background while the guitar is the foreground.
Or perhaps I can sculpt a soundscape from such sounds, some slowly repeating, others coming and going. A walk through a landscape, where the hills are a sound, the trees are a sound, the ground cunching under our feet is a sound, and the distant caw of the crow in the tree is a sound.