Audio randomly cuts in and out on Realtek Digital out

Vista SP2
Realtek HD Audio R2.28

P5KC motherboard SPDIF out via rca cable to a Kenwood VR-5090

I've had this setup working fine for over a year now, until i just came back from a vacation. Now the spdif audio randomly cuts out for a few seconds and then back in. I have no idea what might have caused this. The sound works fine with the pc speakers.
I have tried updating the Realtek drivers, ac3 filter, ffdshow; tried different files, file types, players including vlc1.0, wmp, mpc. All were no go. I've checked the cables, tried a different input on the amp/receiver.
I'm out of ideas, any suggestions?

Dont think so. Its been fine for a long while until just now so I dont think those would cause the problem. The only thing new is we've just switched out all our phones to 6.0ghz, would that be it?