Periodic noise

Every eight minutes? And lasts for ten or fifteen seconds?

If you live in an urban setting or an apartment, discovering the source of this may be more difficult. 

Look at any other wireless devices used around the house. In particular, those that may be close or too close to the hifi. A Wifi router could be one culprit. Another could be a device like a weather station remote or monitoring system that periodically connects to your network. (Or is your neighbors, looking to connect on your neighbors network.) Some GPS devices will have an interval like that to upload a changing position. Others, like those flat, white, locator tabs that help us find lost keys. Camera monitors, refrigerators, light switches, hot water heaters. 

So much of life today is connected wireless. Do you have one of those new thermostats?

These things aren't supposed to interfere but many do. Sometimes the interfering noise may be a sign that the equipment may be starting to fail. Other devices are just plain nasty. I had a Sprint Blackberry model a few years ago that disrupted everything right before it rang. 

Good luck.

Power off any othere dvices in the room you can. Routers, switches, thermostats (if WiFi enabled), cable TV, satellite receivers, etc as well as light switches, wall-wart chargers, anything at all that draws electricity.

See if this helps any.

Next, disconnect the phono stage from the AC outlet.

Fluorescent / high efficiency light bulbs, etc. can also contribute. Let us know.

Erik

Thanks! The noise is periodic and regular, every 8 minutes 30 seconds or so. Therefore, light bulbs, chargers, dimmers, thermostats etc are unlikely suspects. Turning off our wifi router, TVs and mobile phones etc is no help, the noise comes anyway. The noise sounds like wireless interference, it comes and goes a bit (but is not a radio station signal, more like a data packet burst).