Need help with my c2300

I have a question regarding a recent problem with my system. My current system: iMac running iTunes with Amara with IRC > PS Audio NuWave DSD > C2300 > 2xmono MC275's > BW802D1. I just updated to the c2300 (previously solid state preamp) and I feel that it has been a significant improvement in the overall sound of the system. The problem is that when the system is on but nothing is playing, I can faintly hear a classical radio station playing through the speakers (this was not the case before I added the c2300 and is independent of the volume setting on the c2300). I don't notice it while most songs are playing, but it can be heard during really quiet songs (ex. beginning of Pink Floyd Echoes). When I removed the c2300 from the system, plugged it into another outlet and plugged my headphones into the c2300, I got the same radio signal on my headphones. My interconnects are balanced Canare L-4E6S Star Quad from blue jean cable - 6 ft. I have tried switching out power cords, switching power plugs, switched the tubes, I tried ferrite cores (I know... had to try something) and nothing has worked. The whole system is plugged into a Furman Elite 15i power conditioner (which I previously thought of as a glorified surge protector). I bought the c2300 used from an authorized Mcintosh dealer and it was in great condition when I bought it, but I have no idea how many hours are on the tubes. Would switching out the tubes help? Would plugging the c2300 into a separate isolation transformer help? Would tube shields help? Would a new power cord help? I do live in the DC area about 2 blocks from a radio tower (... and my marriage is not worth suggesting that we move because of this...although I thought about it) Any advice? Thanks
You have a tube that has gone microphonic. This same thing has happened to me a couple of times. See if you can order a low noise/tested for microphonics version of that tube from a reputable but reasonably priced dealer such as Tube Depot.