The last time I tried making ground loop suggestions, it didn't go over so well. But I'm brave. I'll try this again.
A power conditioner is only going to help eliminate noise on a line that is otherwise checking out good. First you need to check to make sure the line is good.
First thing to do is check the electrical outlet with
one of those cheapie plug-in testers you can get from a hardware store.
A mis-wired outlet can cause grief. For example, the black and white wires are reversed, the ground is not hooked up, etc. There are a bunch of conditions listed on the test device above, all should be checked. If anything tests bad, call an electrician to get it fixed. Alternately, you can turn off your house power and check the wiring in the outlet yourself, if you know something about electricity. But since I'm writing this, I'm guessing that's probably not the case. So call an electrician.
Next thing to do: get a voltmeter, set it to measure AC first (then DC), then check to see if there is any voltage between the chassis of the noisy device, and a ground. By a ground, I mean for example, a plumbing fixture in the house. You can also test against the electrical ground in an outlet, if you know what you're doing (but I advise against sticking any sort of probe into an AC outlet unless you are very familiar with electricity). If you measure any voltage at all, call an electrician. You have a wiring problem in your house that requires attention. Do not attempt to fix this yourself.
Where I live, a lot of the homes were built in the mid to late 1950's (about the same vintage as the tubes we like to buy). The standards for wiring back then, are not what they are today. Wiring can break down, insulation can stop insulating, or previous owners of the homes could have done stupid crap with the house wiring. I've gone through and fixed many issues in my own house due to the stupidity of previous owners. I'm amazed that people don't hurt themselves more often with bad wiring.
Once you're convinced that your wiring is ok, and you still have noise, then get a power conditioner.