As I read your account I am reminded of an incident while repairing a tape deck on a military base. The repair was a success, but I suddenly noticed a periodic, raspy noise. I was completely flummoxed until, out of the corner of my eye, I noticed that the noise occurred every time a rotating radar antenna pointed in my direction.
I never assume a problem must be [ … ] or cannot be [ … ], else I’ll likely be blindsided. I do, however, play the percentages. My first thought in your case is that there is an external cause.
Are you describing a noise that occurs while playing PORT through the receiver or when a receiver audio output is playing through PORT’s Line-In?
Does the noise level track the Volume control setting? Does the noise continue if you disconnect the audio input to PORT?
Now… that’s a great shout and it hadn’t occurred to me this being RF interference. I don’t know what it might be from and, of course, when I tried to do some tests this evening it wasn’t happening.
It certainly only occurs when the aux input used for the Port is selected, no issues when listening to vinyl for example. If there was strong enough RF to end up on the audio output I’d expect that to be affecting the 47 year old gear rather than the Port. I wouldn’t have thought it would make much difference which input was selected however it’s something to explore.
Historically, the SONOS ZP80, ZP90, CONNECT, and PORT can be easily victimized by ground loops. This is why I suggested disconnecting Line-In.
What is a “ground loop”? We assume that the case and the outside shield of all the signal cables are at the same potential which we assume is, zero, or “ground” for all boxes in a system. If, for whatever reason, one or more boxes are not at ground level, there will be an unexpected circulating current between boxes that can result in unwanted output. Large systems, such as broadcast and recording studios, can have massive ground loops and will hire engineers who make a good living picking through the equipment, eliminating the ground loops. After the ground loops are dealt with, there are very strict rules with respect to adding equipment because the addition might bring ground loops back.
Your observation that the noise does not occur for online music suggests there is an analog ground loop. Disconnecting the inputs will break the loop. A common creator of ground loops in home systems is the cable box. The cable box is part of a system that includes the neighborhood. If there is a grounding issue down the block, you will also own it if your cable feed is not properly grounded as it enters the house. There can also be lightning damage risks too. If you disconnect the cable feed and your noise stops, this is a very strong hint.
Miscellaneous noises can also be induced directly into the cables if the cable passes through a strong magnetic field. This is more typical of turntable signal wiring because the voltages are very low. If the wiring passes close to a power brick or power cable, the brick can induce noise into the phono circuit.
It can require some imagination to track down these little noises. Be careful with assumptions.
Hey, Possibly a slight misunderstanding of what I said.
The issue is definitely not a ground loop, there’s no loop in place, and certainly no general noise just the specific sound I complain about - however I completely agree this could be an external RF interference, possibly with the Port and it’s cable acting as an antenna to the old analogue gear.
The sound is heard only when the Port is selected, it doesn’t affect vinyl playback which is entirely internal to the old Mitsubishi music centre.
The sound is heard whether the Port is actually playing music or not. So it will be heard over/behind music playing from the Port and also when the Port is silent.
I’m still not 100% convinced the sound isn’t coming from the Port but I would need to do more testing and I’m currently away from home so that will have to wait. That said I’m leaning towards this being external RF interference from something outside the house. What that might be, I’m not sure.
If anything is connected to a Line-In or Line-Out, there can be a ground loop. Sometimes the orientation of the power cord in its socket can impact the noise magnitude. If you disconnect everything from PORT and play the empty Line-In through another speaker, the only “loop” left is the power connection. Installing shorting plugs in Line-in is a plus for this test.
You can minimize external noise pickup by being excessively neat with wire management. Placing a metal bucket over PORT or wrapping it in foil can reduce external RF pickup. Be careful with cooling. There could be junk on the power line. Premium surge suppressors can help with this. Pay attention to appliances switching ON and OFF. Of course the timing of appliances can vary with season. Pay attention to neighbor activity.
Now you see why the ground loop consultants earn big money because they need to ask these questions with each box in the studio.
Note that I’m not ruling out a hardware issue with PORT, but given your symptoms, this is not very high on my percentage list. A failed internal connection could elevate PORTS sensitivity to ground loops and RF attacks. My first “ask” is always about the presence of a cable box.
A wired network connection could be involved in a ground loop.
It almost sounds like something from an old space invaders game. It occurs every 56 seconds and regardless of whether music is playing.
I used to hear similar when my mobile (cell) phone was on desk near wired PC speakers, cant remember if it was every 56 seconds, but periodically a similar sound to what you are describing lasting 2-3 seconds.
