Need Help Troubleshooting Ground Hum

I am finally trying to resolve an issue that has plagued the analog side of my rig for a number of years: I get a nasty buzz/hum when I play records. Although it gets louder as I crank up the volume, it is not subtle. It sounds something like the kind of buzz you sometimes hear on PA systems. I am assuming it is a ground issue, although I don't know how to solve it.
You can look at my system page to see my rig. Relevant details: I have a SOTA Sapphire turntable feeding into a Bottlehead Seduction phono preamp. The preamp, in turn, is connected to a Manley Shrimp preamplifier.
If memory serves, I did not always have this hum in the system. I think that at first cropped up a bunch of years ago when I physically rearranged my electronic components.
The hum is always there, but only on the analog side. It gets louder when I switch the turntable on. A couple of days ago, I tried rearranging some of the components and moved the preamp further away from the turntable. It didn't get rid of the hum, but I noticed for the first time that the hum actually gets softer (while the turntable platter is rotating) when I touch the top plinth (nonmetallic) of the turntable!
I understand that these kinds of hum issues can be notoriously difficult to resolve, but if somebody can suggest troubleshooting steps I'd be extremely grateful.
Thanks, guys!