Ground Loop?

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.

I once had a ground loop thet crept up when I had my preamplifier on one circuit and my amplifier on the other. These circuits came from different phases in my main breaker box. When I got the amp and preamp on the same phase the issue went away. Don't know if that helps your situation, but I noticed you had two different feeds for components so it may be worth looking at that. Try plugging all components into the same outlet and see what happens.

One of my friends is a retired electrician and I'm going to get him to give the A/C line a go over. I also ordered a ground loop eliminator from Amazon a Btuty Buzz, if it doesn't work, I'll send it back.

I’d never had a problem with Ground Loop until my wife turned on an infrared space heater in the basement.  I had no idea what was happening and it drove me nuts until I figured it out.  What’s funny is we switched to a regular space heater and haven’t had any issues since.