New Scout 1.1 with hum issues, kind of fixed?

So, I just got a Scout 1.1 off Craigslist from a fellow audio freak. When I plugged it in and got it all set up, I went to listen to a record and the hum was so bad that the table was basically unlistenable. LOUD and overpowering the music, even.

So I did some research. I connected the arm/junction box to the phono pre and that helped a little, but I wanted to try something else. I decided to try adding a ground wire from the bearing nut on the bottom of the plinth to that same terminal on the back of the junction box, and, sure enough it made the hum just a little quieter... so, I went further and decided to add a ground wire from the motor to the same terminal again... same result... even quieter. There is still a very light hum but no where near as bad, and if I disconnect the wires from that junction box, that super LOUD hum comes back. So, this is obviously helping in some way.

Does that mean I need to ground something else????? I'm relatively unqualified, definitely not an electrician... is this normal?