"Buzz" Coming Through Speakers


I have a Audio Research SP16 tube preamp. I recently noticed that without any music being played (or during quiet music passages)there is an irritating "buzz" coming from the speakers. Since the tubes had considerable play time over several years, I replaced the tubes. However, the "buzz" continued. In the past, changing the tubes resolved the problem. But not this time.

I would appreciate any thoughts you might have. Thank you so much.

Kit
kitjv
The audio system is plugged into a general lighting circuit. With all lights in that circuit off, the buzz persists. So a dimmer switch is assumingly ruled out.

I unplugged (one by one) all of the audio/video components plugged into that circuit. The buzzed ceased only when the preamp & the power amp were unplugged.
Plug in a component directly into the power amp leaving the preamp out of the loop and see if the buzz goes away. I presume you have no power conditioners plugged in.
You may try lifting all your cables off the floor, making sure no cables are touching one another, and crossing cables at a 90 degree angle -- not parallel.