Replacing generic RECEPTACLES

Loserbreath must live in a dilapidated rooming house to be so concerned about the structure not being able to dampen reflected sound waves. And being so knowledgeable about the NEC, has ironically created a fire hazard by stuffing flammable foreign materials into receptacle device boxes. But then, box fill is only a concern for “old men that write books of doctrine”, and not a worry for some ignorant people. That sounds like a big liability when it catches fire and burns down the rooming house or group home or whatever it is. Beware of these risks folks, and keep your homes safe by not embarking on fool’s errands.

" I’m a contributing member and I don’t hurl insults at other members."

Very noble stance sw, it might have been your original intent, however as this thread progresses, recent posts have you straying from your said stance.

Nurse! Thorazine! Man down!

Something new to worry about? (man down!)? Anyway I can say since I have never worried about the wires in the wall before, nor know of any realistic plan to ’fix them. I’ll take a total pass on the issue. (Reminds me of various ’net articles of what you ’should’ or ’should not’ be eating so you do not die, or so you live near forever. Just a lot of stuff for the nervous types to ponder. I would bet someone posted about the in the wall vibration just to see if somebody ’bites’.
In other places, seems that small treated crystal chips do ameliorate the problem of both physical and electrically caused vibration. The NCF formula of Furutech NCF labelled duplex are for just that purpose. And folks whom previously owned Furutech GTX-D Rhodium duplex without the NCF, but then bought the NCF duplex, DO report the NCF helps lower noise. Maybe in new construction an audiophile could work on it. Aside from injecting whatever into the walls around the conduit? Not gonna happen in most cases. A problem never before worried about? I am SURE someone will now worry about it. LOLAlso I would think the insulation around the three wire type in wall AC would help. And the usual cord and rubber/ plastic on external AC cords helps also. (No help for Zip cord though.)

Since the subject of vibration through receptacle covers was mentioned, I'd like some advice. The covers on my duplexes are not perfectly flush to the drywall so I'd like to secure them.
  I have two 20A dedicated lines coming from a subpanel, then wired to Hubbell duplexes. I'm using large non-magnetic stainless steel covers which are very rugged.

I want to insulate the inside of the covers to insure a more secure fit. Should I use rubber or Sorbethane, or would there be any benefit in using carbon fiber fabric or tape?
All this talk about buying Oyaide carbon fiber covers has me wondering.