Is EMI noise in electrical system inaudible?

NO! Any competently designed electronic component has been designed with this factor in mind and will be impervious to radio frequency interference (RFI). There is no need for fancy and expensive mains electricity filtering - contrary to the beliefs of the "golden ears" crowd. The promotion and sale of such AC devices is an attempt to profit from the uninformed and gullible. 

These are the same people that will tell you that you need not only an expensive AC regenerator but also an expensive AC cord - and then a hospital grade AC outlet! All  B*LLS**T!