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

@filipm I am not convinced you have a broken or poorly designed phono stage. 

Recap of the evidence so far:

1. You have a predominant 50hz hum in the noise as was analyzed previously.

2. Both the EAR and the ARC LS16 exhibit this noise in your apartment

3. Both the EAR and the ARC have three prong power inlets

4. The EAR routs its ground through the third pin of the power inlet as confirmed by your connectivity test. Presumably the ARC does as well. My Herron tube based preamp, and my Bottlehead tube headphone amp do this as well. 

5. The EAR does not exhibit the noise when used in another location (when plugged into a power outlet not in your apartment)

6. The shorting plugs did not reduce the noise

7. Grabbing/touching the cables affected the noise

8. The troubleshooting guide I linked, Bottlehead's trouble shooting guide, and @hagtech 's guide all suggest a 50/60 hz hum/noise is a lifted ground

This evidence suggests you have a lifted ground, possibly either in your power strip, or in your apartment outlets. Assuming the LS16 is not broken or poorly designed, and exhibits the noise too suggests that the EAR may not be broken. That would not make your EAR broken or poorly designed, just not being used as specified (with a good connection to ground).

Assuming the OP lives in the US, I think it's a bit too simple to blame his issue purely on bad grounding, if you listen to the recorded noise up above.  First of all, there is an intermittent burst of 50Hz noise.  In the US, we use 60Hz AC, and it's pretty well regulated at that frequency. Typical noise due to grounding issues is at 60Hz or 120Hz.  Moreover, it's not intermittent; it's constant.  This noise seems due to RFI or EMI from some outside source, though it's true that the susceptibility to the Interference could be related to a poor ground circuit somewhere.  There are already a myriad of reasonable ideas for the source and what to do about it in this thread.  I hope something works.  I am now wondering about bad diodes inside the EAR or the ARC.  I am also wondering what did happen or will happen when all the tubes are replaced, though that will not rule out a cold solder joint inside one or the other device.

@lewm - an excellent point - I was assuming the OP was on 50Hz AC power, based on one of his previous statements in this thread, and the circular plugs in the powerstrip in one of the pics he posted.

@filipm - are you on 50Hz AC or 60Hz AC power? (should have asked this question earlier.)

I plotted the noise spectrum in Audacity, and the 50hz buzz/hum is constant throughout the entire recording at around -17db though it does have very short spikes to -13db intermittently (I think this is the intermittent bursts lewm is talking about). And then there is another spike of a range of frequencies every four seconds.

From the Bottlehead trouble shooting guide:

"Buzzy hum, like a bee - This usually means a lifted ground connection. "

if a lifted ground, then where it is lifted is the question, but a cold solder joint is certainly possible, though I would have thought if so it would have shown itself when the EAR was used at an alternate location. 

@lewm  @ejb14 I should have mentioned I live in Prague, Czech Republic. The voltage is 230V and the frequency is 50Hz. I posted it on a local forum but got quickly annoyed by the same jokes some people have been posting for the last two decades over and over.

I was in Berlin yesterday and took my EAR along. It worked perfectly fine even with the cheapest power cord and the interconnects I was using here. I didn't get the tubes yet but I returned with an ARC REF150 power amp. What a beauty.

Ejb, I'm now gonna read the article you have sent. Thanks. 

Exactly, if there was a lifted ground on the EAR, it would have been apparent at least at one of the locations I have been to. I wanna try to bring a small intergrated amp and plug it in on the hallway to eliminate the circuit in the apartment.

Is there any test I can do inside the apartment? I invited an electrician and he said the power line should be fine. 

@filipm  You could get an outlet tester from Amazon or a hardware store - one that would show open ground/earth would be important. Search Amazon for "outlet tester Prague" (or UK) - You can also use your DMM to test (google how to do it, lots of hits) - just be careful - and use just your right hand to place the probes - do not use both hands - if the outlet is not connected to ground, you don't want to become the ground. If you can, I would get an outlet tester. They are cheap and a great thing to have in this hobby. You likely want to test your power cords too for ground correctness.

I've been in and tested many homes and apartments. Not all were wired correctly, even the newer ones. Check all outlets.