Yes, the power strip is good according to the circuit tester.
I see what you are saying now about the 3 wire / 2 wire plugs. I do have a DVD player and external speakers plugged in that have 2 wire plugs in the same outlet. I'll try unplugging everything that is 2 wire plugs and see whether or not that helps. The TV is 3 wire, but the receiver has a 2 wire plug though so I'll have to leave that plugged in.
What kind of a meter would I need to read the metal cases for a potential?
EDIT:
I tried unplugging everything in the entire room except the TV and the receiver. Didn't help at all.
I have been looking online and have come across AC hum filters. Do you think something like this would get rid of the problem? I know it's a bit pricey, but I'd really like to fix this problem.
Ebtech Hum X at zZounds
EDIT 2:
Amazon has several reviews that report that their ground loop audio hum / scrolling horizontal video lines were fixed with the AC hum filter I listed. I didn't notice until I turned the brightness really high on my TV that there are also scrolling horizontal video lines on my set when hooked up via RCA/composite yellow/red/white. Same thing happened when I moved the HDTV into the room and turned up the brightness--it did it with the composite cables as well as component, but not the HDMI cable. It sounds like it would be worth a shot to at least try it. If it doesn't work then I guess I could send it back or sell it on eBay. Here's what a few of the reviews on Amazon says:
"I had an annoying 60cycle hum appear after my satelite installer installed my new hi-def DVR. A quick search of the internet led me to the Hum X. Decided to order it but was a bit scepticle. Received in quickly and installed - viola!!! Hum gone!!! I am a happy camper!"
"I don't typically write reviews for products, but I am a technician and I had a ground loop in a television. I spent two whole days working on trying to eliminate the grounding issue and even had my electrician come over and try. Nothing worked. I decided to try this and it worked like a charm. I only wish I had this on the first day. I am going to start stocking these on my truck."
"When I added a new TV to my system I was getting a hum through the speakers. I plugged my power amp into the Hum X and the hum disappeared!"