My appreciation to everyone for their serious advices.
Answer to Lloydedee21:
"Is it possible the tubes are slightly microphonic, and your speakers are picking it up? Have you tried tube dampers? Borrow some if you can before going out and buying. Sometimes when a tube is microphonic it will pick up certain noises either internal to the tube due to vibration or due to vibration in the room outside the tube...and translate it as distortion thru the systems signal."
I do have dampers from Herbie's Audio Lab on all tubes so I assume no issue with microphonic effect.
Answer to Lloydedee21:
"Is it possible the tubes are slightly microphonic, and your speakers are picking it up? Have you tried tube dampers? Borrow some if you can before going out and buying. Sometimes when a tube is microphonic it will pick up certain noises either internal to the tube due to vibration or due to vibration in the room outside the tube...and translate it as distortion thru the systems signal."
I do have dampers from Herbie's Audio Lab on all tubes so I assume no issue with microphonic effect.