I have a weird buzz issue; can you help me solve the problem?


Hi - my integrated amp has a 25db persistent buzzing noise; I need help figuring out how to solve this problem.

Here’s my system:
CODA CSiB integrated amp - custom tuned to produce 25w Class A power before switching to Class B
Lumin T2 streamer/DAC
Dynaudio Focus 380 speakers
Audience AR2-T2 power conditioner w/Audience power cable
Audience AU24 speaker cable
Cardas Clear M power cable
Purist Venustas Luminist Revision RCA interconnect
Synergistic Research TeslaPlex SE outlet
Shunyata Venom Defender

Some background:
I’ve had the CODA integrated for about 5 years. The remainder of my system has come on-line subsequently (I had different speakers initially). Within a few months of purchase, I noticed a buzzing noise coming from the speakers whenever the amp was powered on (bias “on”), but no noise in standby mode (bias off). I took it back to the manufacturer, who plugged the amp into their dedicated circuit and it was dead quiet. I had the same experience taking it to a local audio shop. Thinking that it might be a noisy circuit, the local shop loaned me a lesser priced solid-state amp (I forget which brand) to bring home. I hooked up the shop’s integrated to my system and.....it was dead quiet. Now I was confused. 

A dealer loaned me a completely different system with a tubed integrated, different speakers and cables. There was even a worse buzz coming from this system than from mine. I went back to living with my system and forgetting about the buzz.

Fast forward 4+ years. I have moved to a new house in a new state. Unfortunately, the buzz remains :-( I even tried plugging the system into what the electrician was sure was one dedicated line in the house (it was in the kitchen, so I had to run an extension cord to where my audio system lived). Still, the buzz remains.

I really love the sound of my system, but this persistent buzz is a (ahem) buzz kill (sorry for the predictable and bad pun). 

I would love to get some thoughts on what I can do to get rid of this damn noise. Please help!



mwsl
So, here’s a weird one. The input shorting plugs arrived today, so I installed them (for the heck of it). Not only did it not impact the buzz at all, but.......it prevented the amp from generating any sound until I removed them all! Now I know for a fact that I’ve had more than one input connected at one time (I only have one currently), so I don’t get it. 

Can anyone explain this issue? Is it at all related to what might be wrong with the unit?
@ mwsl

Did you by chance plug the shorting plugs into an output? Inputs only.

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I guess the 'solution' will be found by borrowing some gear, including all your wiring and cables, and patiently swapping out til the ugly duckling is revealed. It's not rocket science--just patient organized evaluation )
UPDATE: have spoken with CODA. They have heard of the buzz issue before (has something to do with the jumpers on the circuit boards). They said that pre-2015 units had about a 25% chance of buzz. The owner gave me instructions to bypass and test the jumpers. Unfortunately, despite my hopes, the buzz remains after having tried the suggestions offered. 

I will be sending the amp back to CODA.
Are you using singe ended cables for it?

Did you try a isolation transformer to see if it would fix it?