Intermittent electrical noise in system

and... is anything about 15 years old or more and might electrolytic capacitors in it?

The noise oscillates on and off about two seconds on and four seconds off continually. The sound resembles the voice of a cricket.  It's not loud but it's constantly there intermittently in the background in soft passages.
My components include an old Conrad Johnson pre-amplifier (just checked out by a technician who found no noise,) new Rega Planar 3 turntable, Grado Sonata cartridge,  NuForce dual amps, Theta DAC, Oppo BluRay player used as transport and Dahlqust DQ 20 speakers.
There are no neon signs in the vicinity. I don't know any appliances that cycle on and off like the noise does.  It's maddening!  So much so that I avoid playing records.

That interval seems like it could be a beacon of some kind. 

If there is a wifi router nearby, turn it off and see if the noise disappears. If it does, see about moving any wifi gear away from your hifi or using ethernet instead of wifi. 

Look for recent electronics you've added to the home. Wireless weather stations can interfere like this. So many products now have wifi capabilities. Bluetooth also. Argh.

If you're in an apartment, good luck.

Have you tried disconnecting all the digital sources and just running the turntable?

It's fixed!!!!
Thanks be to dbtom2!!!!!!