[mythtv-users] OT Eliminating a ground loop/hum

[gLaNDix (Jesse Kaufman)]

sorry for the long post.  i realize this is continuing an off-topic 
thread and if there may be a better place to post this, let me know :) ...

anyway ....

I have a similar ground loop hum problem caused by the coax in my house. 
  according to my surge protector and line tester, the outlet IS 
grounded properly.  instead of the hum coming from my sound system, it's 
actually coming from my TV speakers (the tv is always turned all the way 
down).  If i mute my TV, it's gone completely, however i have subtitles 
if i watch TV normally! :(  i turned down base and treble completely and 
pushed the balance all the way to one side, so it's at least only coming 
out of one speaker now, but i'd like to eliminate it completely.  here's 
a quick rundown of my setup:

for regular tv:
coax -> surge protector -> tv

for regular tv audio:
tv (RCA) -> sound system

for dvds/movies/myth video:
myth frontend (component) -> tv

for dvds/movies/myth audio:
myth frontend (spidf coax) -> sound system

all components are plugged into the same UPS except my wireless mouse 
charging station.  it's in the same surge protector as the coax.  both 
surge protector and UPS are plugged into the same outlet.  if i connect 
the incoming coax directly to the TV, i get a TERRIBLE hum (nonstop) 
from my sound system as well.  i tried a different surge protector w/ 
the coax and i got the same hum, so this surge protector must be doing 
something different to help cancel out most of the hum, but it's still 
not 100%.

before we moved in, the previous owners had satellite, so the cox guy 
used the same section of cable that came from the satellite to the 
inside (which really pissed me off, since it could've been done with one 
long run instead of two spliced together w/ an inline connector!!!). 
the satellite had a grounding block on it, but when the cox guy did his 
run, he removed the ground block (that was grounded to a copper rod in 
the ground, presumably the standard 8' but who knows).

it looks like the cable box in the back of the house (where the line 
from the telephone pole comes in) has a ground wire running inside the 
house, but i'm not sure where it goes from there.

any suggestions?  should i try getting a new ground block and replacing 
the inline coax connector with it and re-connect it to the ground rod?

i also have a line coming in the "server room" in our basement where my 
myth backend is.  would it be worth trying to ground that? (it has a 
splitter so one line goes to my modem and the other to the backend).  or 
does it have to be on the actual line going from the cable box on the 
back of the house to my tv?  the myth backend goes into a different 
circuit and is on a UPS but does not have the coax running through a 
surge protector.

also, i've seen some sort of "caps" that go on unused coax jacks that 
claim to reduce hum (they're metal and screw in just like a coax cable). 
  anything to this or just a marketing gimmick?

if it matters, i'm only using standard def (the cheapest level i could 
get) of cable ...

one of the main reasons i want to get this fixed is that i've noticed 
sci-fi comes in much better when running directly to the TV and not 
through the surge protector.  (w/ the surge protector, it has diagonal 
lines running from the top right to the lower left that move from 
left-to-right).  it's the only channel that has this, however.

jesse