As someone who is very much into heavily distorted guitar with long feedback loops, I appreciate your comment (especially for the insight). I'm a huge fan of doom/stoner/sludge/psychedelic metal (and all variations of those), where distortion and feedback are often used to create sounds that are difficult to notate. Combined with progressive metal/rock, which is heavily reliant on that jazz/rock fusion, and you get entire genres built around the harmonics and odd sounds that show up from lots of distortion.

I feel that Sunn O))) - named after the amplifiers, are a great example of slow rhythm music that relies upon heavy distortion and feedback to create the atmosphere and primary sound of their music. This is just a modern band, but the experimentation and techniques go back to psychedelic and acid rock from the 1960's, and mostly center around Black Sabbath as "the" band that really created the prototype for the sound.

Monolord, Bongzilla, Acid King, Bongripper, REZN, and SLEEP are some great modern examples that fit what you've described.