Many years ago when I had a TT I must have been lucky. Never had any issues with hum on my old AR, B&O, a couple of Duals and finally my Micro Seiki. Throw in in some super cheap Technics, Fisher, etc. Never any issues. Without knowing what you've tried I would
1) move TT to a second system to see if problem follows TT....maybe its your preamp's phono section that has the issue
2) relocate TT away from large transformers
3) move cables away from large transformers
4) try isolation transformer on TT ac line
5) check cart wires from cart to rca jacks
6) try cheater plugs on certain equipment to reverse plug polarity
Did this just start?