Ground problems are the worst. Sometimes it can take a while to sort them out.
The original post states "Different TT but still has the issue whether it's connected or not." So, this means that you get the noise with no turntable connected? The way to test for sure is to short the phono input. If the noise persists it's not from the TT, connecting cables, or TT ground.
Here are some other things to try to see if there is any change:
(1) Use the standard AC plug to ground the line preamp and then use "cheaters" to lift the ground for the phono stage and the power amp.
(2) Use a separate single wire to connect the ground lug from the phono stage to the ground lug of the line preamp.
(3) Use a separate single wire to connect the ground lug from the phono stage to the house AC ground (can use the center screw of AC socket plate).
(4) Use a separate single wire to connect the ground lug from the line preamp to the house AC ground.
Maybe you can find the magic combination. Best of luck.