Unsure How to Fix Based on Resonance Plots

I just finished tensioning all the belts (around 8 or 9 lbs based on frequency) and tension plots are absolutely horrid. I don't even know where to begin to start with this. I checked all the pulley gears and they look to be centered with the belts. I do hear vibrations, with the loudest being the base plate (plate covering the bottom of the machine). When I put my hand on there it damps out most of the vibration noise. But it still sounds like there is slight rattling noise. On my T0 toolhead I have the orbiter runout sensor installed and am wondering if that is contributing to the rattling noise. If i listen closely, it almost sounds like the balls in the linear rails that are rattling. Is it also possible some of the t-nuts for the linear rails (or any other t-nut I guess) didnt actually rotate properly and ended up not gripping the frame? I don't know how I would even tell since I can't look under the rail into the channel of the aluminum extrusion. The screws all seem tight though, nothing loose.

It looks like the Y belt plots are much much worse. The X plots look at least acceptable. The whole structure seems to shake between 50-70Hz (rough estimate) during the Y belt process. I have the machine sitting on a quartz countertop so I assume thats pretty decently flat.

I've attached my belt tensioning and shaper results for reference. All of these steps were performed with both CoreXY and hybrid belts attached, since it looks like IDEX does not work without the hybrid belts.

I also wanted to mention, I did a bed mesh probe and it seems reasonable for my Vcore4 400 (about 0.2-0.3 total deviation across the bed), so my assumption is that the frame is decently square. Not sure if that makes a difference but just throwing it out there.