CATV Coax Ground Loops are fairly common....but might as well check entire system:
These are much better articles re Ground Loops and what can be done to eliminate them:http://www.cinemasource.com/articles/gnd_loop.pdfhttp://www.audioxpress.com/reviews/media/AE600HA.pdf
1. First of all, if you have power being supplied to your "system" from wall sockets on different sides
of the room, use power strips so power all comes from same wall socket....but don't overload it...
If there are separate feeds from the breaker panel, this might help.....but it's a long shot....
PS: If you buy power strips, be advised that our local Home Depot carries the Belkin brand,
most of which include RFI/EMI Noise Filters in addition to high energy spike suppressors.
2. Connect grounding wires between your various A/V components, esp. from those that don't
use 3-prong plugs to one that does....if it helps, make it permanent....I do this anyway to avoid
loud pops and hum when I disconnect audio cables.
If your house doesn't have 3-prong sockets, you could upgrade (IF AND ONLY IF) you already have
a safety ground wire to the outlet....otherwise think about alternative grounding methods....
3. Disconnect cable coax. If the hum goes away, it's a cable ground problem.
First make sure the cable coax is properly grounded at the building entry point
(an NEC code and safety requirement).
If that doesn't eliminate the hum, try a CATV Coax Isolation Transformer, such as the fol. ISO-MAX:http://www.avsupplystore.com/jen-vrd1ff.htmlhttp://www.cs1.net/cables/jensen_transformers.htmhttp://www.jensen-transformers.com/d...1ff_manual.pdf
Note that CATV needs both extended LOW frequency AND high frequency response,
so be wary of cheap knockoffs...
However, if it's a cable ground loop problem, I would call the cable system to fix it....
4. If it isn't the cable feed, there are isolation transformers for power, video and even component video:http://www.jensen-transformers.com/iso_vid.htmlhttp://search.cablestogo.com/?qu=iso...%20transformer
and "hi-fi" audio:http://www.audioxpress.com/magsdirx/...n-galo2706.pdf