Intermittent buzzing coming through speakers

Recently, my speakers have been buzzing on and off. They'd buzz for 30 or so seconds and then go back to silent for a while. I tried plugging my amp directly into the wall outlet, to my RSA Haley power conditioner, and finally adding an EbTech HumX between the conditioner and the amp, but it's always the same result. I can actually hear a similar sound if I put my ear to the power amp itself. Thanks!

 

Have you tried it in other sockets? in other buildings? Is your amp a cosy home to some much-worn caps?

 

If the transformer is buzzing, it might be a dc offset.

You really want to test the stack somewhere else before you drop moolah on a dc blocker or isolation transformer, tho.

 

What else is on the same circuit? Has anything new been plugged/wire in? Do any of your near by outlets live on another breaker?