I have the same issue in my house too.
It is a ground loop issue.
I put a piece of copper tape from the metal chasis of the preamp to the shell of the output RCA jack (ground ) and did the trick.
Adding a small .47 cap from output RCA jack ground to the chasis also did the same trick.
Hope this helps
TT might not be the source of the bad ground.
It is a ground loop issue.
I put a piece of copper tape from the metal chasis of the preamp to the shell of the output RCA jack (ground ) and did the trick.
Adding a small .47 cap from output RCA jack ground to the chasis also did the same trick.
Hope this helps
TT might not be the source of the bad ground.