If you are having voltage sag problems on you line, you should notify your electric utility at once in writing. mention the problem and state clearly that you believe that this is a safety issue. That buzz word "safety" triggers the utility to come out and do something. They will test the voltage levels and noise on your line for period of days to see if there is a problem, and if they find a problem, they will fix it.
You have to submit something in writing and mention safety.
If the noise is coming from equipment in your home, you should try to identify the culprit and fix that problem.
Do not that any recommendation that starts with "float the ground" on equipment. The ground lead is there for a very good reason. Your safety. If you have a ground loop or buzzing, we have discussed this many times on Audiogon and there are ways to isolate the equipment that is causing that problem.
Do not float grounds. You are asking for trouble if you do so. Find and fix the problem. Bad interconnection cables that tie signal return to the shield, bad grounding schemes in a piece of equipment, equipment that share the neutral and/or grounds before they go back to the panel, and many more reasons.
I have noticed that some electricians do not bring the hot, neutral and ground all the way back to the panel when running dedicated lines. They may share the neutral and/or ground with other feeds.
Trust me, there is a reason why one has ground loops/buzzing or pops, noise. Sometimes it is difficult to find the culprit. But systematic searching will isolate the problem.
Be safe, don't take the advice of people that tell you to float the ground. You can do that for a quick minute, just to find which piece of equipment may be causing the problem, but do not leave it that way.
enjoy