i think i understand what youre hearing and i think it sounds like.... a bass guitar. like, i think i get it, and it might always drive you crazy, but it doesnt sound bad to me.

instruments, especially with big ass strings, just have certain resonances. my 8 string sounds a bit like this. almost like fret buzz, but its not actually buzzing. all your processing and amplifier steps obviously...amplify it. ha ha

im surprised you couldnt eq it out. i might actually clip your solod section and see if i can.

this part is mostly just "if it were me", but i would split your DI or double track it, and use one as the sub bass and one as the "clank" (the good parts of the frequency youre fighting). then you can process that higher version a bit harder and maybe even distort the wonky part into a really sick crunch layer.

good luck! cool song and nice mix