I’m not sure if mine is an x-100 or x-101 but I found the best grounding point to be the top of the pre tower. It’s located behind the left side of the face plate and has two tubes mounted horizontally. There is an exposed grounding wire connected to these two tube sockets and I used closest screw to this point to ground my TT. Your unit may not be the same as mine though. Also, if you haven’t done so, try reversing the power plug in the outlet or a different outlet if available.