Take a serious look into the Quantam ElectroClears.
I live in a high rise building and had installed 3 ElectroClears. The sonics and television picture had improved significantly. And, the improvements didn't include any tradeoffs. They cost only $50.00 each, and work extremely well in cleaning up your AC line to improve your audio and/or video system.
This was "the best" reasonably priced addition I've experienced.
Chris