One last ditch effort before I return this set. I am wondering if a power conditioner could fix the problem! I emailed an ISF Calibrator who blogged about floating blacks. Here is what he said:
When I calibrated that 700U, the reduction in floating blacks was a bonus I was not expecting. Normally, there is no way to address this problem. It lies in the engineering of the TV. With plasmas and CRTs, blacks float because of the quality (or lack thereof) of the power supply. In the case of the 700U, I use the service menu to adjust the grayscale and sub-brightness. Sub-brightness is a finer way to tune black levels than the user menu Brightness control. It also raises and lowers the threshold of the user Brightness control. My theory is that the blacks float less because I was able to lower the user Brightness substantially after grayscale and sub-brightness adjustments. I also lowered the Contrast quite a bit. Contrast and Brightness interact quite a bit on this TV. To get a good gamma curve, Contrast has to be lowered a fair amount. You’ll notice that as you raise Brightness, there is a threshold where the adjustment leaps up substantially. Try to stay below this point. Lowering Contrast will bring this threshold down. You might be able to reduce the black float some by watching the interaction between Brightness and Contrast.