I do hear a hum through my amp during the wee hours, but that hum is normal as it is the noise floor. The noise I hear is more of a buzzing/clicking.

The PC's PSU has an audible buzz from the physical device while the amp is giving off the buzz on the audio signal. I've also tried turning off my PC, DAC, pre, and amp during the phenomenon and I think even with only my amp on I can still hear the buzz through the audio signal. I'll have to try to turn off my PC again to make sure.

I think my PC's PSU and amp are particularly sensitive to some sort of change in the power. I know nothing else in the shared power line is being changed when this happens.

I don't understand what you mean by rotating the mains plugs by 180 degrees.

I do hear a hum through my amp during the wee hours, but that hum is normal as it is the noise floor. The noise I hear is more of a buzzing/clicking.

The PC's PSU has an audible buzz from the physical device while the amp is giving off the buzz on the audio signal. I've also tried turning off my PC, DAC, pre, and amp during the phenomenon and I think even with only my amp on I can still hear the buzz through the audio signal. I'll have to try to turn off my PC again to make sure.

I think my PC's PSU and amp are particularly sensitive to some sort of change in the power. I know nothing else in the shared power line is being changed when this happens.

I don't understand what you mean by rotating the mains plugs by 180 degrees.

I'm telling you... modern PSU's, motherboards, and video cards have changed in production and this is referred to as coil whine.  It's super common and doesn't seem to be getting any better.  You can try out different video cards or PSU's or motherboards but it's going to drive you insane.

What he means by rotating the plug is to flip it upside down, not possible if it's a three prong plug or if one plug is larger than the other, in which case you can use/make a cheater plug.  But it's probably not going to make a lick of a difference.

If you are hearing the noise on your speakers/headphones you can also isolate the amp itself IE no sources connected to the amp to troubleshoot.  USB line noise from the PC sounds terrible and is easily audible in the chain.

One source of 'noise' are 'old' or damaged power strips with spike suppression that has already suppressed one too many spikes.


These plug in strips are nearly invisible in that we can all to often take them for granted.
When the MOV's or transzorbs give all (or even some of their all), they can then become noise sources.  And they add their noise right at the end of the distribution system, into the neutral and ground, right where we plug in our other gear.


Some of these plug in strips have 'replace me' indicators, but that doesn't mean it always helps.  Others (usually the cheaper ones) have no such indication.


There are also cheap house lighting dimmers that spew spurious harmonic noise when they are not full on, (when actually dimming the lighting load) as well as the electronic temperature controls for stoves and ovens, etc.


And sometimes just tightening up the screw clamps coming out of each circuit breaker can make a difference.  They can and do loosen up after repeated thermal cycles.  Also you can pull the wire out from the circuit breaker and make sure it isn't corroded before you tighten that circuit breaker screw clamp back down.


And lastly although there are the main feeder cable clamps for the power cables, both the 2 phases AND the neutral line that connects up to the ground buss should be tightened/checked as well.
These circuits are VERY DANGEROUS and should only be messed with by those who know what and how to do so. 


Electrocution is possible for ANY of the above, take appropriate cautionary measures.


Lastly is the ground that is being used by the panel itself.  Some household grounds are in poor shape and so the neutral lead from the pole plays a major role in providing a 'stable' ground.  This usually doesn't work very well as the ground from the pole is more directly modulated by the rest of the power distribution from its step down transformer.


One simple test is to measure the dc and ac voltage and frequency riding between neutral and ground at any power outlet.  It is best when all of the equipment remains plugged in and the voltage is tested while the equipment is both on and off.
This test does require decent a DVM and knowledge about what are acceptable readings.  But suffice to say the voltages found between ground and neutral should be small and stable.  If you have access to more sophisticated test equipment (scopes, power meters, frequency analyzers etc.) these can shed additional insights into the electrical environment.


Also some electricians are less 'sensitive' to the needs of an especially 'quiet' power distribution system.  They are used to dealing with high voltage circuits, not low voltage situations where even 1 volt riding on top of the neutral line can be a killer for tweako audio systems.


Just a few thoughts


JJ

I guess there isn't much I can do about it then...

There may be a lot you can do about it but you will have to isolate the problem first.
I have outlined the steps in my previous post.

First see if your amp shows the problem without it being connected to anything else but speakers/headphone.
Then connect the next item etc.
So find out when the problem occurs and under which conditions.
From there on you can look for a solution.

IF it only happens occasionally and in a very short time frame you need to find out when that is.

If you are on a good relation with your neighbour try to get him to switch it on and off while you are listening or keep it on while you are testing.
When this is indeed the problem it is time to find out what is causing it (pollution or DC on the AC line) and then you can take measures.

Does gear with a real traffo in it suddenly hum audibly from its enclosure at the same time ?

Does the pre-amp or DAC have a headphone out and does this hum as well ?

If the PC has it's own sound card with HP out does this hum audibly on the HP out ?

The amp hums in both channels when nothing it is not connected to anything except mains ?