Faint buzz in speakers

I'll throw my guess into the ring: Filter cap on it's way out. Oh, and don't neatly coil excess cable carrying signal.

PS- Modern dimmers, including smart dimmers are not noisy the way the old one's were, mechanically or electrically.  You certainly can have remote controlled mood lighting in your listening room. 

I had a similar problem a few years ago.  In my case I had a subwoofer and I had to ground the sub plate amp to the preamp.  It cleaned it up

Some amplifiers are noisier than others, efficient speakers will bring this out. However, if you can't hear anything from the listening position I would leave it alone and enjoy your music. 

Since "Can only be heard with ear right up to drivers" it is not a "problem."

The solution to the "problem" is simple, don't put your ear up to the driver.