Replacing generic RECEPTACLES

The Blu Tack is only on the backside, NOT front of cover.Previously I have experimented with small quartz crystals. I bought several pounds of small tumbled quartz (average 2mm to 4mm size) all sorts. And applied my own idea of a coating, Automotive dielectric grease. (never ever get in eyes, or on hands soon in eyes. bad bad)
(what is wanted is to coat the crystal bits with a non conductive coating. Some have cooked the crystals in whatever..The idea is the individual crystal bits get radiated energy and then vibrate. dissipating the energy, instead of allowing it to continue to radiate, they ideally need to be in close contact, but not inter-conductive.) Placed in small baggies. stuck them all over the place. Anyway got kind of tired of that. But when I have been doing the Furutech outlets, I used some of the baggies. They in a way, are like the NCF material on some Furutech duplex. So yes there are small baggies of treated quartz around some of the Furtech duplex in the boxes and in the Furman power conditioner. (I previously had them in the Furman, six years? no problem) I also have some baggies taped to AC plugs, and ALL the Furutech plugs have as much of the treated quartz crystals inside as I could pack in.(and still close up the plugs)

I get that the Blu Tack is only on the backside, that's where I want to use damping material. 
So, I intend to stop vibration at the receptacles, but do you believe that this area also needs treatment for RFI?

I'm not going buy carbon fiber treated covers, but I'm still looking for an explanation of how RF can be generated or exist at the AC receptacle.
 

The 'pressure' of 120v AC is 'pushing/radiating' electrons off the surface anywhere the voltage is available. in use or just sitting!.(same thing IN equipment, where the AC line comes in, switch, etc, around the transformer... endless)
I own a small tool to measure radiated fields. (Greenlee GT-16 adjustable voltage detector $25 or so at Amazon) It registers off equipment displays, even individual diode lighting, any powered outlet spews out this stuff. So do ALL unshielded power cords. It is also carried along metal. So say a pole lamp with a zip cord AC wire inside, but not touching, up to top? the whole pole is charged and radiating the field. Only insulating/shielding the wire will stop the field. The quartz crystals do also stop it, but only if they are more tightly packed. if they are only jumbled.loose. they do not stop it, it manages to get through. So no matter what, your duplex outlets ARE radiating a field. The outlet cover may be designed to stop it from inside the outlet box. The HOLEs in the outlet cover are spewing the stuff anyway... but the moment you add a plug, the plug body is ALSO radiating the field, unless it is fully shielded! any plastic plug body is letting the field radiate off it. Metal too, unless the metal is grounded.           
This stuff is almost unavoidable. and takes a LOT of effort to control fully. No one does this and they all survive. Plus you have endless RFI in the air anyway just at higher frequencies. TV over the air, radio, police bands, cell phone, Who knows what else..I have over 30 WiFi signals floating through my apartment. None of which belong to me!It is kind of a hidden problem, since you do not feel it. But the stuff is there, all the time all around. (no big deal) so trying to control it?? tough job. Fancy duplex outlet covers are like a small band aid on a big wound. (so are the quartz crystals.. but they are way cheaper than the fancy duplex covers, and far more versatile) I suggest buying  a Greenlee GT-16 and find out for yourself. (the Greenlee is a little better than the other similarly priced tools like it, though when it's battery gets half worn, it starts to go crazy, replace the battery!)Anyway, hope that helps.

Thanks so much, Elizabeth, terrific explanation. Now it makes sense why you have the quartz crystals in different areas, and why so many tweaks are for sale to treat these same areas.
  I was aware of possible RFI being found in the obvious areas such as unshielded AC cable and transformers. The Crystals and similar tweaks to be used system-wide seemed unnecessary to me.
The Greenlee tool could be useful.
Thanks again.

It’s a common misconception that crystals generally operate by absorbing RFI/EMI. In fact, crystals operate in most audio applications by absorbing vibration. For example, in room corners, in proximity to ekectron tubes, on output transformers, on top of tube traps, and on cable connectors, wall outlets and windows. The only good vibration is a bad vibration. Having said all that I wouldn’t be very surprised if someone somewhere could find a place where crystals improved the sound by absorbing RFI/EMI.