1.) Are any splitter ports unused (either nothing connected or cabled to an unused jack)? If so you should terminate the unused port(s) with a 75 ohm termination plug.
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2.) Is there an amplifier installed in your system? If so, remove it as your first test. You have more than enough raw signal strength at you location - An amplifier would likely overload and cause mixing and distortion of the desired signals... not a good thing.