I had to put isolation feet under my Xfinity cable box to quiet the fan noise down. Doesn't eliminate it but does quiet it down quite a bit. Hope this tip helps you.
Noise from Xfinity cable box
I just installed an Xfinity X1 cable box in my rack with my audio and video gear and it is the noisiest piece I have ever had in my system. I think it is a fan, but it runs constantly, even with the power switched off (standby mode?). I had been using a simple little digital converter from Comcast in the system that worked fine for HD video and audio, and was dead quite. I am thinking of going back to it and ditching the DVR and voice capabilities. Anybody else have this problem with new X1 cable boxes?