I understand your thinking. I had the same thought because I started with the same firmware version as you but had problems listed in that update and four in the other updates. They are all gone down now, including power spike issue. I did one thing that I died not mention. I disconnected the speaker cable, cut it and made clean new area. It is a habit I got from working with a friend installing speakers. He told me it solved alot of problems when you have low end speakers with generic cable.
If the problem still persists try changing the cables that you are using to connect the audio from your source boxes (DTV/Cable/DVD etc) and see if that makes a difference. I have a friend that complained about speaker feedback on powerup. I determined he had a defective HD Cable Box from Time Warner Cable. They gave him a new box (new cables) and it works fine now.
If you try all of this and it still does not resolve, get it exchanged, PDQ. As mentioned there is a 15 day window for the rebate. I filled mine out today (12:15AM) and will put it in the mail later today.
Good Luck all!
Another helpful hint I read about in the threads here is for SD TV through cable or SAT is to put ratio into ASPECT mode. It does not look perfect but is a big step up in quality, especially fast moving sports action.