Power conditioner needed????

While you're looking over your grounding, check carefully for loose &/or corroded connections. Disassemble the clamp where the ground wire connects to the rod. Burnish the top of the grounding rod with a wire brush, emery cloth, fine sandpaper etc, exposing clean bright copper. Burnish the bare end of the ground wire too. Before reassembly, liberally apply some silicone paste such as SilGlyde (NAPA auto parts supply shop) or NoAlox paste (electrical supply shop or larger hardware store) or even automotive or marine bearing grease will work; this prevents the connection from re-oxidizing. Also check & clean the opposing end of the ground wire; whatever it connects to. Look for loose fasteners, apply paste, snug down the setscrew, etc. Check your house power ground also, if you can access that. Check the neutrals & ground conductors in your house power distribution box and all conductors at the load outlet for tightness & oxidation.
You say ground rod(S), as in more than one? Multiple grounds could be a cause of ground loop noise, as per Jim above. This can also be a lightning electrical hazard due to differences in ground potential. You could try running all connections to a common ground post, or tie them together electrically with reasonable size conductors (#14 awg solid).

isolating the coax by connecting two antenna matching baluns directly back to back (available at Radio Shack)

A balun is a simple RF transformer. 300 ohm balanced twinlead connections at the (typically input) side (usually connected to a TV or FM antenna)
and 75 ohm unbalanced coax connection at the other end (typically output) side; they will work in either direction though. You would need two as my previous post. Ask at Radio Shack. Also available at Lowes, Menards, Ace Hardware.

If you don't understand RFI etc & want to learn more, then link to my Audiogon member email & leave me a phone contact. I am a federally licensed RF technician.

You may also check for info on Audio Asylum. This is their tech dicussion section.

http://www.audioasylum.com/cgi/tv.mpl?forum=t2

Finally...............the solution! When my Oppo DVD player is connected to the TV with the DVI to HDMI connector, there is distortion whether the player is turned on or not. The problem is worse when the player is turned on. Using the component connection eliminates the problem. It took HOURS of trouble shooting to figure this out. Now, the question is why. I tried grounding the Oppo box and cable...........it made no difference. I see no difference in picture quality using either connection, so I am ok with leaving things as they are, but I can't help but wonder what went wrong. The set up was unchanged for about year and then suddenly the distortion appeared. Even when it is at it's worst, it comes and goes.
Thanks to all who have helped with suggestions. Without your help, I would have run out of things to check and given up.
Btw, while going through the breaker box I did find several loose connections. A worthwhile undertaking if you are qualified.

congratulations on your perseverance John. This is hardly the first time that someone has resolved an issue without really understanding exactly what happened & why. I was thinking though, if you have further problems with the DVD player you could (1)replace it or (2)have it serviced (for possible degraded capacitor in the power supply) or (3)try an AC line isolation transformer, for power to that offending component only.

I had some screwball/intermittent noise problems with my computer, which I unsuccessfully tried everything that I could think of to fix. I ended up buying a small-ish (3 amp) isolation transformer on EBay for about $25. It was originally designed for homeuse medical equipment. What this does is float the power supply such that neither side of the AC line connects to household grounded neutral. Easy fix, but I don't know what / why either.

This is Solder meister and I see that the Breaker Panel was mentioned.And yes many times when you have lose connections in a house this can cause the electrical system to interfere with audio and video equipment. I would recommend tightening your screws every say 3 yrs to avoid this. If you are comfortable and you are qualified to do this as getting across the wrong connections can be shocking. Also if you are building new or have access through a basement or open wall you can run separate electrical line to your home Theater system 15 amp should work fine I have personally one to the equipment rack one to the Sub and one to the Projector and house lights. It works wonderfully but not all have this option. Good Luck.