I left the surge protector on.
That protector was recommended without any numbers. Numbers say why it does nothing. For example it ignores everything on 120 volts until voltage well exceeds 330 volts. How often is your AC spike above 330 volts?
Noise is not a surge - ie single digit or maybe as much as a few tens of volts. Learn how this is made irrelevant in all other electronics. Rip open an electronic power supply to see filters on its front end. Using both inductors and capacitors - not resistors.
Learn about different types of currents - longitudinal and metallic. Your filter must also address common mode currents. Even better is to completely remove that filter from an old power supply. Now you have a front end filter designed by someone who actually knows how electricity works. Who is not so naive as to recommend near zero plug-in protectors.
Of course, best noise elimination starts at the source. More facts to consider if decisions are tempered by numbers.
CAT 7 does not do anything more than CAT 5. Again, too many recommend without first learning what anything does. Had they first learned numbers, then a recommendation would have been obviously bogus.
Another way of getting an engineered solution is to create 5 volts from a wall wart type power supply. Either a well regulate 5 volts wall wart. Or do what most electronics do. Get a poorly regulated wall wart. Then use the single chip power supply regulator to clean and further filter out 'dirty' electricity.
Plenty more answers are possible. Too many to discuss without further details. But this should be obvious. Any answer that is not tempered with perspective (ie numbers) is best ignored. That includes the surge protector, Cat 7, that resistor / capacitor circuit, and even discussions of the various current modes.
We make mistakes to learn. Now learn from mistakes including why a surge protector, et al were tried.
A problem must be first defined before any of these numerically defined solutions can be recommended. What is the incoming and a completely different outgoing path of that offensive current? Without first defining a problem, then any solution is called shotgunning. Shotgunning is done when one has virtually no useful knowledge - as indicated by answers that don't say why with numbers.