Dedicated 20 amp lines/should i use a sub panel

Hello,
I have a question for this group regarding an issue likely related to power that I face time to time in my music room. It seems that audio/video quality fluctuates during the day/evening and I get the best quality (audio/video) only after midnight. I have two dedicated 20 Amp circuits (10 gauge wire) with a pair of Furutech receptacles which feed all of my AV components. I don't have any power conditioner but use a Nordost power distribution unit. My system is relatively quiet with no 60 hz hum. However there a slight hiss that comes out of my Aerial Model 7T speakers when everything is powered on but it is only audible if you take your ears very close to the tweeter.
Could anybody comment on the possible root cause behind the inconsistent audio quality throughout the day?
I am thinking of installing a balanced power transformer but not sure if that (isolation) would address the inconsistency issue. I would love to hear your opinion on this as well.
Thanks.

@noromance/@lak,
Thanks for your feedback.
It seems like the hiss coming out of the speaker tweeter is a non-issue and in-reality that's not bothering me at the moment. So I would ignore it....
However turing off all lights/heaters/furnace etc is not going to be a realistic solution... Would a balance power transformer with its so much advertised common-mode-rejection functionality be able to  address the inconsistent A/V performance issue during day/evening? These items are expensive and relatively difficult to install, specially the units that connect to a 240V power supply. That's why I wanted to get an idea from this group before getting started on this project. For those who have this or similar power issue what do you do to avoid/eliminate it?
Thanks.

@Al- Yes, it makes sense to measure the voltage to narrow down the issue. I haven't upgraded the Parasound Halo-A21 amplifier because of two issues, room acoustics and power quality inconsistency issue that we are currently discussing. I have somewhat handled the room issue with GIK hybrid Alpha panels and wanted to ensure a good clean power feeding my music room before spending any money on the electronics. I have more or less decided to go with Pass Labs XA100.8 mono blocks when I am able to resolve these issues. 

@Peter- Is it worth spending $10K to get a branded transformer from Equitech or Torus instead of getting a Commercial Power isolation transformer at a much cheaper price?

Thank you all for responding to my queries.