Faint buzz in speakers

If this was my system, it would be rewired, use different outlets. If anything is 2 prong, instead of 3 prong, swap the cord around. On 2 prong power plug, swapping the plug around can have profound sound differences. 

Of course make sure there are no lights turned on, on that circuit, signal cables are away from power cables.

Might also be your amp needing some service, like bias adjusted, or a component going out of spec. 

Or, that self respecting audiophile could simply make sure all lights with dimmers are turned off while listening.

I noticed that sometimes it's a light rheostat (sorry, dimmer switch) 

Any self respecting audiophile should get rid of all dimmer switches in the house.

I noticed that sometimes it's a light rheostat (sorry, dimmer switch) making noise in the circuit. However, it's usually a cheap charger that is the culprit in the circuit. 

I have had this problem twice. Once, it turned out to be proximity to a router. When i removed it from the room, the problem went away. 

The bigger issue turned out to be a defective toroidal transformer in my amp. The manufacturer replaced the transformer, and the problem ended. As someone said, sometimes our power, or the system doesn't agree with one or more of the pieces. But sometimes, it really is a definable local problem.

Someone once said to me many decades ago: "The goal is not the absence of noise, but the presence of music." Since then, I don't sweat things I can't hear from my listening chair. 

David

I had the same problem with a krell amp I had. 
I just took care of the problem. I sold the amp. It wasn’t jiving with my ac current in my house. It was fine for the guy I sold it to. 

Thanks to all who’ve chimed in about the buzz in both speakers. Perhaps it does sound more like white noise than a buzz. No, it is not audible from my listening position 8 ft away. In fact, it is so faint you have to place your ear right up against the cone to hear it. I don’t know which is more annoying, the noise itself or the fact that I’ve been unable to track it down. I’ll be sure to  try your suggestions this weekend when I have the time. 

Before tackling the audio interconnects, disconnect any video or ethernet devices. An RCA out to a TV that has a satellite cable in or an HDMI from another device plugged in elsewhere can be the problem. The additional shielding on “better” ethernet cables, like CAT-7 instead of CAT-6, can also be the problem. Ethernet is itself by design fine. But the shielding on a cable can be the problem...

Re: bug zapper comment above... yes, keep it off the house ethernet ;-)

Check the bug zapper in the garage 

@OP Some amplifiers have small amounts of residual noise thought it should usually manifest itself as white noise, but there can be other noise as well. It is also possible that one or more of your noise reduction devices are causing the noise - including your balanced power unit. Take them all out of circuit and introduce them one by one. If the noise is still there after that, its most likely the amp itself. However, if you can't hear it from the listening position I wouldn't sweat about it.

@jmfinney I had exactly the same issue! After replacing US brand pre+amp with Accuphase C2420+AD2820 + P4500/A48, such noise disappeared! 

Two things to try.  Turn off every other breaker in your home. if that makes the problem go away you may have some device introducing DC. This happens when a device/appliance sucks more on one side of the waveform than another.  Often in very cheap DC supplies.

If it's still buzzing, disconnect all inputs. 

I had a buzz or ground hum years ago, and after trouble shooting with the dealer ended up installing some gadget between ac cord and wall outlet that fixed it.  It was called 'Magic' something.

A search found this:

https://ifi-audio.com/products/gnd-defender/

More than a 'cheater' but still retains safety of grounding.

I had the same insidious problem. It was caused by the ground plug. Even though it is NOT recommended to use, I simply installed a ground plug adapter and eliminated the ground prong. It worked. Buzz was finally gone!

It was the ground plug on my pre-amp that did it.

Be aware you are eliminating an important safety feature when you do this.

Gold Note IS-1000MKII integrated amp. Does not fluctuate with volume. Ever so slightly louder (still very faint) in right speaker which is closer to amp. Have not tried removing all interconnects yet. Also, when all breakers in house except stereo circuit are off, same buzz still there.

Type and brand of amp?

I recently had this issue with a new amp and it was my cabling picking up some noise. In my case the amp only accepts RCA connections, so this may not have been a problem with a balanced setup. Is it in one speaker or both, and if in both, is it the same level? Try turning off the amp, remove the interconnects, turn back on, is it still there?