tube rush detection help

thanks newbee. i've swapped all the tubes from amp to amp, and the hush stays. i've also taken a computer duster air canister and blown whatever dust might've been in the tube sockets but the hush stays. it sounds a lot like white noise you get on those break-in discs, only not so prominent. doesn't change with volume. stumped.

OK, i disconnected the source, still get the rush. And yep, I swapped all the tubes out for the tubes in the other amps, and still get a rush. Going to try again tomorrow, maybe I missed something. Tubes have been used for two years now, so the power tubes are due to be replaced anyway. Tho it doesn't look like it's the tubes, at least not that I can see...