UPDATE: Problem 100% IDed:
Got a tip on the possible source and it turned out to be dead on. We have a NETGEAR powerline adapter hooked up to get internet from the back 1st floor to the front 2nd floor of our house. Disconnected it tonight and the noise was 100% eliminated from my phono stage. After hearing the suggestion I started searching the problem on the www from that angle instead of from the Rotel angle, and I found out that this is a very common problem. Now at least I know the source of the problem, next issue is how to keep good connectivity throughout my house and still use my phono. That should be solvable, now that I know what to solve. Learning this saved me from buying a new phono pre, or worse, a new full preamp - neither of which would have made any difference.