Hum due to old electric wiring in new apartment

I recently moved to a new place with very old electric wiring (I guess around 1960's). I would like to clarify from the beginning, that there is NO possibility to change / redo the electric wiring in this apartment, because it's only a temporary place for me to stay (a few months to a few years) and the landlord is not willing to invest anything.



The situation is as following :



My location is Vienna, Austria and the electric wiring is only 2 wires (230V) without any RCD and no safety earth connected to the outlets. 230V are stable and have been measured on the outlets.

I ordered a couple of P-RCD to put on the power outlets to at least offer an RCD and safety earth connection after these outlets.



I recently tested a Pultec clone connected to my interface on the same power outlet with a simple Furman Power strip (no power conditioner).

As soon as I touched one of the aluminum knobs, I got main hum in the signal path. If the knobs are touched by a non conductive material, there is no hum. I tested the same gear in another location and everything was fine, so it's definitely a problem with my electricity in the new apartment.



I was wondering how this is possible and how I can solve this problem.



The facts :

- The Pultec and the interface are not connected to main earth because of lack of safety earth wire on the outlets.

- There is the possibility that the safety earth prong is connected to Neutral inside the outlet, as this has been done a few decades ago. I haven't verified this.

- Signal ground is connected to chassis ground via XLR pin 1.

- As soon as I touch the knobs, chassis ground is grounded thru my body to the floor. (right ?)



Any ideas ?

I'm very thankful for any help !

Hum due to old electric wiring in new apartment