Amp transformer buzz/hum from DC on AC line?

As of the last while, I had a buzzing/humming sound coming from my Plinius 9200 integrated. Fairly loud - I could hear the sound from 5 or 6 m away in my listening room - but didn't seem to affect the sound from the speakers. There was always a very slight buzz from the speaker, but you had to hold your head pretty much up against the speaker with volume at least 3/4 (with no input!) to hear this. I attributed it to normal operation.

During my early period of owning this amp, same thing happened. Conctacted the Plinius rep and had a replacement torroid supplied for replacement; Plinius acknowledging there were issues with an early run of the torroids. Solved the loudness of the torroid, with a minor but still present buzzing persisting. Thinking my recent problem may be a hardware issue again, contacted Plinius. This time, they suspected DC on the AC line. While somewhat suspicious, for no sound reason other than what occurred the first time, I decided to start checking this out.

Long and short, this thread among many, arrived at the suggestion of using the Humbuster III to handle any DC (if any present). Picked up one and it arrived today. Put it in line with the Plinius, sparked the system up, and no noise whatsoever. I had to put my ear against the amp to confirm the status 'on' light. A couple of hours of listening to some familiar material, no veiling or change in the sound of the music. In fact (and I think this is my mind at play) I thought there was a slight increase in detail and ambiance in some of the solo piano recordings that I had been listening to. And I should add that slight hum in the speaker that I attributed to normal operation is no more.

For $200-odd bills, an incredible device.

An update to my previous post.

Listening to a wider spectrum of music while using the Humbuster III, the amp still is dead quiet. But I have also found that the unit removes a very slight amount of detail from the music, what I'd call a slight reduction in higher frequency. Most notable on the leading edge of acoustic string, voices. And by this it affects the definition and air about the same.

I'm going to continue playing for a few months and see if it's a case of needing burn in (always suspect of that, but had a good example of it a while back with an upgrade of power cords and better IC's). We'll see. Nice to see the hum removed, and the amp is running cooler, but not happy with the cost of doing that.

Someone had mentioned in this forum something about this unit that was contrary to what was thought as it's sole efffect i.e. DC removal. The documentation with the unit states 'over/under voltage surge protection' so I'm not certain just what goes on within and if something beyond the DC removal contributes to this attenuation of detail.

Do we still think the humbuster filters some higher frequency detail from the output of the amplifier?

One thing I can say is that the humbuster works well on toroidial type transformers, but not really on EI types. There may be some exceptions, but that's the effect I have noticed on a variety of amplifiers and other gear.

Are you sure it's not related to a dvr motor running? Not sure if you have a dvr but they can cause a racket if not isolated.