Originally posted by gonk:
How is the coax cable routed? Is it running parallel to a power cord for some distance? That could generate some interference that not even a well-shielded cable could entirely escape, and it would manifest as a hum or buzz simply from having the coax cable connected to the 990.
No interference in a digital signal can cause hum. Digital is data, it's there or it's not.
This is obviously a ground loop issue. Computers/cable modems are often causing such problems.
One easy way to eliminate the issue would be to use an optical link, as it provide total galvanic isolation between the two devices.
Regards,