It is rare that this is needed, but you may benefit from monitoring the incoming AC voltage, if you use a power conditioner put it after that.
See if the voltage really is changing when you hear a difference, and monitor the N-E to make sure it stays low.
If you see either changing a lot that may be either a problem or a need for a regulator. That unit is $20, btw. :)
While I do use 100% Furmans, what I didn’t mention in this thread is that I use a Furman wiht AVR (Automatic Voltage Regulation). It doesn’t do much here, but in past gigs in apartments it was often active. That feature is expensive as it requires big iron, and sometimes has mechanical hum, so I don’t necessarily recommend it for everyone.
Now that I think about it, that unit was more active in late Spring than it is now. Could be that they've improved the power delivery and I didn't even know it. :)