Adding to what Brian said, it sounds like your system WAS working perfectly, and then started having problems relatively recently.
It sounds to me like you have some noise-generating (or signal-sucking) electronics, which are contributing to (if not entirely causing) your problems.
While a phase coupler is a good thought, it might be causing more harm than good, especially if it is passing that noise across the phases.
I'd suggest you looks for the sources of the noise first, then try to fix them. There are some really great troubleshooting threads here on the forums, and you're probably going to want to do the "breaker box test" (turn off one breaker a a time until the problem goes away or gets better) as a first step.
Pay attention to any electronics that were added around the time the problems started, as well as any CFL bulbs that may have been changed. Just about anything can be a noise-maker or signal-sucker, and it will take some detective work to find the culprits and filter them out.