ground noise isolation

Refrigerator cycling on/off?
Fluorescent light?
What's a smart meter?

Are you in a single family dwelling / duplex or / appartment?

Sometime neighbors can generate some nasties on a power line, even the next door variety.

2.5kw iso transformer will work OK and should be good up to 1000 watts but only if the power factor of the load is high enough.
Does your kilowatt run ok now, from the wall?

Viiu,

I am not sure what kind of regenerator you bought. From your description, it sounds like an UPS (Uninterrupted Power Supply) designed for computer. If so, it is not a good idea to use them in audio system.

UPS generates dirty power. It was designed to keep computer running in case of power outage. It wasn't designed to provide clean power. It actually does more harm than good in an audio system.

The noise problem you described sounded like a loose ground wire somewhere, probable in the power outlet. If it were a ground loop problem, the noise should be constant, not intermittent. Ground wire and connection could be corroded after 15 years.

I have no experience with smart meter. Can you tell when its on/off cycle starts? If it coincides with the buzz, than it is the most likely cause.

Just a thought.

I had the problem before I purchased this regenerator. I previously owned another regenerator without the battery. I had too hoped that the regenerator meant clean power.

It has been suggested to me that house wiring is not properly grounded but nothing has changed in fifteen years. My local utlity has finally turned on the smart meter and I suspect that may be at the root of my problems. It cycles on and off for about fiftenn minutes each hour.

Go to your local hardware store and get some adaptors that go between the outlet and your cord end that deletes the ground prong.

The whole purpose of a regenerator is to give you clean power.
I don't understand why one would add noise.Maybe the noise is the unit turning off and on to keep the battery charged?I hope somebody could give a reason why this is supposed to be
acceptable.