Hello OP,
Please unplug that. Further reading will give reasons why, but unnecessary.
I would be hesitant to sound a whistle on an otherwise lively discussion, but we have essentially anonymous posters making reckless assertions having nothing to do with fact. Moreover several are only their ‘observations’, based loosely upon their personal incomplete understanding. I’m not getting into a flame war with other posters by repeating inane statements and then responding. But please unplug your contraption. No EE or state license-holder is going to suggest leaving it as a temporary solution. It’s creating more of a hazard than you think regardless of the sound. I will explain exactly what is wrong with your approach rather than point you to some roundabout explanation not based in safety, science or fact. Of course, no one can exactly diagnose your audio issue remotely. Not doing that. Don’t want you killed or anyone running around your sound room.
In terms of significance these issues are in no particular order. First, at the core, even if that idea of a ground were acceptable, you are using temporary and under-gauged wires. The RCA connectors probably a thinner gauge wire than what a normal ground ‘plug’ wire would be. The-wall ground wire is around 14 gauge (green wire). For an actual ‘ground’ you wouldn’t want moveable, unplugable pieces (RCA M/F) that could be confused with the same cables serving as interconnects. If it’s only you living with the sound room and you can always remember not to unplug ‘those’ wires, it’s still not enough. You have male to female connectors that might have oxidation or be different metals…you should have just wire, or at least soldered or crimped connectors…the ground or “a” ground is safety. In a car you don’t have to remember to turn an airbag on or off. Secondly, whatever was “solved” with approach wasn’t solved but rather relocated. You might have an offending appliance on a shared same circuit having nothing to do with your audio equipment. Additionally to that, there are EM fields everywhere on current carrying devices and a slight move of a cable or wire could have created an issue. Guitar amps can hum based upon a guitar’s proximity to the amp due to the type of pickup used. It’s not the amps fault. Even if it’s a $3,000 amp, depending on the setup it can hum and will. Single-coil pickups.
Thirdly, a “ground” is not the same as a neutral wire (or where the current goes ‘out’ from your devices). The ground is a safety belt mostly for the equipment. It can help save humans though. Conversely, GFCI’s are SOLELY meant to save humans from accidental exposure and some fire hazards but even those are not 100% and must be periodically tested. “Ground” or “Earth” in electronics is not the same as a “green ground wire” or ground hole in an electrical outlet. “Ground” in electronics is a limitless sink which would absorb any voltage so that a predictable “potential” or voltage can be provided within a design. DC, best display by household batteries do not have “ground”. They have “+” and “-“. They also don’t kill. Household batteries are nearly always limited to under 50V because larger exposures can be lethal. In your amp, you have high voltage. AC is more lethal than DC at high voltages but you wouldn’t want to touch 300V of either. Designers of electronics don’t really care or specify whether the “earth” means flow to neutral or ground. It’s nearly always neutral bolstered by a ground, but that’s that what they focus on. Someone will say, “Yeah, my service panel showed me different. I saw that all the white ‘neutral’ conductors at the bar shared a connection to the ‘ground’ bonded to my cold water pipes and a giant copper rod that cost $300 to have an electrician install before he’d put in a 200a panel for another $2,000.” That is true, but not the only story. Those “ground” connections are a last resort of protection in case there is voltage within your house and the neutral conductor to the utility is disconnected. Undischarged capacitors are an example of that. That is fact and science. They are required or rather ‘supposed’ to drain within a certain time limit but there can be older equipment or who knows what people do to hotrod their systems.
I would try to figure out what changed system-wise to isolate a component and eliminate the problem that way or you have a piece of equipment with a problem (or a wiring problem, or competing load on the same circuit…any recent wiring work?).
I remember a comment mentioning a “single” wire flowing into a selector and logically, the “ground” then must be the equipment case. There are some minimalist systems and DIY pieces that do that. You can’t have voltage without a potential between two points. HOWEVER, the voltage running through the selector to the case is 5V at most if there are small lights or its in mV if just signal. Most electronics have a relay or other mechanism to soften the transition. However, if you had the ability to interrupt the voltage from tubes to the speakers without a temporary sink, the circuit board will melt, capacitors explode because with tubes that electricity can’t be in limbo. Say if you held it in between states and there was no relay or resistor. And, it’s not the high lethal voltage in the amplification stage NEVER running through tone controls or volume or gain controls. The high voltages in any system don’t go first to the chassis and then wherever else, doesn’t matter. They ALWAYS by design return to the neutral and as a safety at some point there is a ground wire connected to the chassis, but also the ground on a 3 wire connection. There are rather cheap test device that will confirm if you still have a “good ground” at your outlet. Tubes, solid state or not even an amp. Same issue. You are putting 115V or 120V in and expecting a result...which is not expected to be 120V or higher into your body or a burst of flames.
To go on, but probably the most important notion is that a ‘ground’ is the last resort. And it’s really meant to save equipment. Electricity will run through the path of least resistance. If a short or surge occurs that completely melts your RCA “ground”, it will try to travel through the next thing….a human body, a pet…anything creating a new path. You’ve now created a new path, maybe more preferable, that if water gets in, a piece of wire, a paper clip, a short from an internal component fail or solder fail could be unpredictable. Those interconnect areas are supposed to be very small voltages and completely unattractive to stray voltage. Accidentally leaving a system on and something overheats? I would also not purchase a “box” device to do something your system already did but then something failed or was repositioned to create an actual or apparent issue. Your ingenuity is great but in dealing with any voltages over 50V its best to do in a controlled environment or get solid PAID advice.