Super Noisy Phono Pre--Help?

I have a Fosgate Signature Pre. I feed it with a Lyra MC cartridge mounted on an SME V arm. Until last week, all was bliss. Then the preamp started producing a random popping sound and a motor sound like there was poor electric motor plugged into the same outlet. I thought it was a tube, but swapping out tubes didn't change it. I took it to my local service department. They cleaned and resoldered some of the connections. Now the popping sound is gone, but the constant motor sound persists. The motor sound goes away if I disconnect my turntable. I can influence the sound by moving my interconnects around. I cannot change it by relocating my preamp. It seems like it might be some sort of interference, but I can't understand why it has shown up all the sudden after a couple of years of perfect sound. Suggestions, please. Could there be something wrong with my interconnects or my cartridge?