Professional (and generally speaking) audio equipment can produce undesired sound effects if there’s any voltage irregularities going on. I know that certain outlets in my house that cause static noise out of a guitar amplifier because they aren’t.. perfectly wired? Also, I know audio engineers will typically plug their equipment into an outlet that is separate from their computer to avoid this as well. I haven’t studied electrical or sound engineering too deeply but I have noticed the same. Knowing that this is a general issue, I did a quick search and found this: http://www.enjoythemusic.com/magazine/manufacture/0712/
Oh yeah I have a electronic music studio for years and a clean power source is the beginning of everything. Brought in stuff for repairs only to have the technician tell me that there was nothing wrong. At home same problem again. "Try plugging it in directly to a wall socket" problem solved. And with lots of outboard gear you get lots of cables and lots of adapters.
Google "balanced power for tube amplifiers" and see how far that rabbit hole goes ...
(And it's not all superstition, and it's not all for tube amps -- it's all in the SNRR of your power stages for every piece of equipment in your sound chain.)
