AC power is a funny bugger and it helps to understand how “noise” gets onto the line. Basically noise are tiny “spikes” imprinted onto the sinusoidal AC wave from various sources. Use of a scope can show this. I have a Flintstone era Tektronix tube scope which I use and shows this clearly. Some of the worst offenders in residential are motors (with brushes such as vacuum cleaners), compact fluorescent lamps (the self-contained pigtail type which can cause over 100% harmonic distortion on the neutral) and any electronic device which requires a large inrush current. Also remember that most “noise” is running on the utility lines themselves due to harmonics imparted from various sources mostly large motors.
A dedicated line may help and the use of hospital grade aluminum clad MC cable may help due to the sheath acting as a shield against RF. IG hospital grade MC cable uses a second ground (green with yellow stripe) and with the use of an IG receptacle may eliminate some noise off of the line. This is used for sensitive hospital equipment located in ER’s, ICU’s, CCU’s etc. The extra ground wire is connected to a separate isolated bus bar inside of the electrical panel which is then connected to the ground bus.
A residential whole house TVSS (transient voltage surge suppressor) will eliminate some noise, protect sensitive electronic equipment, not costly, easy to install and only requires two spare circuit breaker spaces and a dedicated twenty ampere two pole CB in an electrical panel. An isolation transformer (1:1 ratio) connected to your equipment may also help on a dedicated line by isolating both the hot and neutral lines from the utility but the ground will not necessarily be isolated. An isolation transformer is rated in Volt Amps (not watts) and multiplying the voltage times the required amperage will give a good estimate of the size needed (120v x20A=2.4kVA) but will not take into account the small losses due to coil efficiency (power factor).
Unless your equipment requires it and you have an extreme case, I cannot see why anything larger that a 20 ampere 120 -volt dedicated line would be necessary using the above methods. Of course some experimentation will be needed to get it to satisfaction. Remember that most equipment and utility grids are 60 to 80 years old and modern upgrades to generating, transmission and distribution have not taken place mostly due to exorbitant cost. Utilities are required to provide power but not necessarily clean power. (My background is an EE degree from PSU some 40 years ago, am a licensed electrician and worked with many local hospitals and utilities in design build). Hopefully this will shed some light on power line carrier noise.