OP, read your post and I have experienced a similar issue (and commented on it before) with TT/LOMC and hum/hiss in background. I know how frustrating this was for me, and feel your pain.
My problem was caused by my wireless router and likely poor insulation on my ethernet cable to my streamer. I was at the same height and about 6 ft away from my TT. When I disconnected and it totally, the hum went away. I relocate the unit to the floor about 20 ft and haven't looked back.
If someone has already mentioned this as a possible fix, my apologies for not reading through the posts.