Thanks everyone for your help. I haven't had time to try everything, but based on these responses and info from another thread, I've done some additional experimentation:

I discovered that if I slightly loosen the coax cable going into my cable box, the hum disappears. I’m still getting a signal, so this appears to be a reasonable workaround. I’m wondering if there are cables available that specifically address this problem.

I experimented with different HDMI inputs on the TV, and seem to have found one that works. Most of them are labeled “4k 30hz”, but one in particular seems to work. The others work very intermittently. In the instances where the TV won’t recognize the signal, I usually see nothing on the screen - merely a message that it can’t find the signal. However, one input will show a green screen. Additionally, sometimes the audio drops out when it will not recognize the picture. Assuming that the “good” input continues working, I am content for now. My backup plan was to buy a new Blu-ray player with two HDMI outputs, and run one into the 975 and one into the TV (my current player is an old Sony BDP-S550, with all firmware updates). Maybe a newer player would eliminate the handshake issue anyway. However, I’d rather wait until 4k players become available.

I’m not sure whether the HDMI cables are high speed. I’ve tried several, ranging from 2-4 years old and 3-6 feet long (all from monoprice). In all cases, the cables were good going directly from the Blu-ray to the TV, and worked fine from the 975 into the old TV.

Thanks again!

Edit - I forgot to mention that I am running a native signal through the 975.


Edited by mtomer (12/07/15 10:34 PM)
Edit Reason: forgot to mention