Tube PHONO preamp interference - RFI, EMI, bad grounding?

have you tried eliminating the ground, period.

MP 200 is poly alloy cartridge and in theory is like a moving iron cartridge. I had a similar issue and eliminated the ground and the pulsations and noise went away. This was with a tube phono section from Audio Hungary. Went SS now with SPL.

If it is louder near the floor, could it be the source of interference is in your downstairs neighbor’s apartment? How many floors in your building? 

Another thought, it might be worth investing or borrowing test gear that would allow you to positively identify what type of interference it is. For instance, if @theaudioamp is correct about it being a demodulation, perhaps an oscilloscope trace could prove that. just a thought. 

For Noromance, I would agree with your idea. Just because I recently;y got a new TV (air) antenna that had a built-in filter for WiFi frequencies. IT cleared up a lot of degrading interference. I would also suggest that Philipm looks at his neighborhood to see if anyone has recently added an Illegal CB radio amp or even a HAM operator putting up something new. HAMS are almost ALWAYS agreeable to helping you find a resolution to any interference from their Radio station. EVEN if their equipment abides with the FCC laws. In days gone by the Phono cart itself was one of the biggest offenders acting like an antenna. I also liked the Ferrite rings idea. THat has stopped many offending signals. I have them everywhere and even MY OWN HAM equipment does not get in the way of quality sound from my stereo. If the tinfoil ides had some effect, THat is the first thing I would replace with High-grade shielded Cartridge wires. I really liked the answers here. Not so many people talking stupid or trash, but helpful responses. I will probably get blocked for saying something nice about the site.

@filipm it’s unclear to me what you tried with wifi? Did you physically unplug from the wall all your routers, access points, extenders, devices that receive and or broadcast wifi and Bluetooth? Turned off all mobile devices (including phones, smart watches, tablets, computers)? This will help identify the source inside your apartment. You said if you lift the unit up the noise reduces? This can mean your downstairs neighbors have some sort of a device that can produce this interference. There’s just too many things…smart switches, smart devices, wifi access points, etc

Also, how old are the tubes in the unit? It would be interesting to change the tubes to something like latest production JJs or Gold Lions. Since you didn’t experience this with your solid state phono stage, if you don’t find and can’t eliminate the culprit, one of the simple options will be to go back to a solid state phono stage.

@esarhaddon , that is not HAM or CB. You can tell it is packetized data and/or for packetized processing. The keeps are the demodulation of the envelope. I will see if I can extract the frequencies of the "beeps" as that may provide a better clue of the source. Some items have well defined packet frequencies.

@audphile1 , the change that is described by the op, appears to be a rapid change increase raising above the floor, then the change stops happening about 5 feet up. The floor is likely acting like a shield, but it could also be ground plane effects, or an inductive current loop.

@filipm Amazon has clamp on ferrite bead kits.
https://www.amazon.com/Tamicy-Pieces-Ferrite-Suppressor-Diameter/dp/B08BPHCXR3

Unfortunately it can be tough to get proper specifications of anything on Amazon. Different clamps work at different frequencies. Digikey will cost you more, but you know what you are getting. For $20 though, start with Amazon. Based on your comments about the output cables, put clamps on all wires input, output, and AC. Due to stray capacitance, every wire can act as an antenna.

@filipm , are you in a high-rise apartment building?  The reason I ask is they often host large cell tower arrays on the roof as well as antennas for other radio types.