@trdcorolla
Hey just a wee thought from my experience - I had a hum, and tried all kinds of things to get rid of it (including replacing the flux capacitor) which didn't work. It wasn't until a long time later that I noticed that my sliders (OPOR for an LX) were touching the foot well body metal - such that there was a direct metal to metal connection between the frame and the body. I lowered the sliders a bit so that there was a healthy gap between the two (so I could squeeze a finger between them), and the hum went away! Man I was so happy - but also frustrated about how long it took me to find it and all the things I tried. So....I guess be smarter than me! I suppose its possible a rock on a trail pushed my sliders up into the body at some point.
On my bolt on OPOR sliders the vertical clamping surface that the u-bolts attach to/thru are pretty tall so it was pretty easy to have them touch the body foot well pan and the frame at the same time. I guess there's a lot of vibration/noise that is in the frame that doesn't get transferred to the body when the two are sufficiently isolated.