Power conditioners

Power problem effecting only left side? I don't buy it.
Something else, cable, upstream component, haunting..... is to blame.

I aggree switch cables and see where the issue is maybe a week tube or a bad connection.

I doubt if your problem is fixable with a power conditioner.

I really doubt a power conditioner is going to fix your noise issue. If it were originating from AC, you'd hear it in both channels.

Check your source component. If you switch left and right ICs, does the noise switch channels?

Are your speaker cables and IC connections good?

Rule out any problems with your amp and preamp. Do you have replacement tubes to install to make sure they aren't the problem? It's not uncommon to have intermittent noise with a tube that's going bad.

Again, I doubt this is AC.