Yup, nodes. I had a nasty one around 300hz. Same thing, could hear it standing up but not seated.
Move your speakers around. Experiment. Move them closer to the walls, then further. Move thrm up and down if possible. Different stands for temporary testing might be good. Use chairs or whatever else that you can use as trmporary stands.
Move your listening position around if possible.
I went from being -6db from 30hz all the way to 200hz to 0db to +3db from 28hz to 200hz just by different height stands and speaker placement.
Move your speakers around. Experiment. Move them closer to the walls, then further. Move thrm up and down if possible. Different stands for temporary testing might be good. Use chairs or whatever else that you can use as trmporary stands.
Move your listening position around if possible.
I went from being -6db from 30hz all the way to 200hz to 0db to +3db from 28hz to 200hz just by different height stands and speaker placement.