high frequency intermittent noise

Actually the new hot spot is Hudson Yards, that is where new construction is happening.  But I hear you, our infrastructure is falling apart.

@james1969

You said in your OP the wall outlet your system is plugged into does not have an equipment ground. Not sure if it will help, or do anything, but there is a good chance the mains branch circuit wiring is installed in steel rigid metallic conduit. (Though it is possible it could be old steel armor BX cable). If it is steel rigid metallic conduit, that would be an acceptable equipment grounding conductor means. (Of course depending on the low resistance conductivity of all the electrical, mechanical, connections made with the lock nuts in the conduit to metal boxes from the metal wall outlet box all the way back to the metal box enclosure of the electrical panel the branch circuit is fed from.)

Does any of your audio equipment have a 3 wire cord and plug? (2 straight blades and a round ground pin).

I assume the old wall receptacle/s in your home are polarized 2 wire that has one straight blade slot longer than the other. Or are they really old non polarized where both slots are the same length?

How are you feeding your audio system from the 2 wire duplex wall receptacle outlet? With a grounding type 3 wire cord and plug receptacle outlet strip? If yes I assume you are using a ground cheater, (3 prong to 2 prong plug adapter), so you can plug in the 3 prong plug into the 2 wire wall receptacle. Is that correct?

By chance do you own a multimeter or access to one?
If yes set the meter to AC volts auto or a scale closest above 125Vac.
Insert one test lead probe in one contact slot hole of the wall outlet and the other probe in the other contact slot of the other in the same outlet. You should read a good steady 120Vac nominal volt reading. If not recheck your probe to outlet contact connections. Make note of the actual voltage reading.

Next.

Insert one meter test lead probe into the shorter of the two straight blade slots of the wall outlet making a good contact with the contact of the receptacle. Touch the other meter probe to the center screw of the duplex outlet that holds on the cover plate. (If the screw is covered with paint scrape off the old paint exposing the bare metal screw head.)
Does the meter read a good steady 120V nominal volts? Yes? If not make sure the two meter probes are making good contact and check again. If still you do not get a good steady 120V reading insert the test lead probe in the other contact slot of the outlet. Do you now get a steady 120V reading on the meter? (If yes the AC polarity is reversed on the outlet.) The voltage reading sold be the same as the reading you measured from the plug in contacts.

So, if after all the above you measured a good steady 120 volts, from the HOT conductor feeding the duplex wall receptacle outlet and the center screw of the outlet that holds on the cover plate, that means the metal box the outlet is mounted to is grounded to the metal enclosure of the electrical panel that feeds the branch circuit to the outlet.

**Note.
That only means that the equipment ground is present. It does not tell you the integrity, conductivity, of the equipment ground’s ability to carry any ground fault current back to the electrical panel in the event of a ground fault event. What it should do though is furnish an earth ground for the metal chassis/metal enclosure of your audio equipment that uses a 3 prong grounding type plug.

IF, after all the above has been met all that you need to do now is connect the green pigtail ground wire from the ground cheater to under the screw head of the 6/32 screw that holds on the outlet cover plate. For a better connection I would remove the duplex cover plate and install the fork of the green pigtail wire under one of the 2 screws that fastens the outlet to the metal box. Check both mounting screws to make sure they are snug and making a good mechanical/electrical contact from the outlet to the metal box.
**(Do not try to remove the outlet for a look inside. The wire conductors inside the box could be really old and the insulation that covers the wires old and brittle. Just you trying to pull the outlet from the wall box could cause the insulation to fall off the wire.)

Next.
With the multimeter test/check the plug strip to make sure you now have an equipment ground.

Last final test! Did it help stop the noise. Or was it all a waste of your time?

Jim

@jea48 Funny you should mention socket outlets, I just changed my socket outlet from a generic to a Furutech outlet (audiophile brand).  When I opened up the original socket, there were only 2 connections made with no ground.  That is how I know there is no ground.  I looked in the socket for a ground wire and did not find one, so when I swapped out the outlets, I simply mirrored the previous installation - no ground wire to connect.

james1969 OP
246 posts 11-13-2017 12:15pm

@jea48 Funny you should mention socket outlets, I just changed my socket outlet from a generic to a Furutech outlet (audiophile brand). When I opened up the original socket, there were only 2 connections made with no ground. That is how I know there is no ground. I looked in the socket for a ground wire and did not find one, so when I swapped out the outlets, I simply mirrored the previous installation - no ground wire to connect.

Just because there was not a ground wire in the box that does not mean the equipment ground is not present. If rigid conduit was used per NEC code the conduit is an acceptable grounding means. The conduit is the equipment grounding conductor. (Of course the rigid conduit must be electrically continuous from the outlet box all the way back to the electrical panel. It can be connected to other metal boxes and conduit bodies in it’s travel.)

Note. Just because NEC allows rigid conduit to be used as an equipment grounding conductor that does not mean your city electrical inspection department does. The AHJ (Authority Having Jurisdiction) has the final say.

Buy one of these.
https://www.homedepot.com/p/Power-Gear-3-Wire-Receptacle-Tester-50542/206212329?cm_mmc=Shopping%7cTH...
It will tell you if the receptacle outlet is grounded and if the Hot and neutral AC polarity is correct. It will not tell you the conductivity integrity of the equipment grounding conductor to carry ground fault current back to the electrical panel in the event of a ground fault event though. Not matter if the conduit is used as the equipment grounding conductor or a ground wire is used.

@jea48 Thank you for all your expertise.  I will pick up that receptacle tester and check it out.