I was surprised but changing my TV2 from 30 to 21 made a big difference in pq. I'd also combined my antenna and satellite signal with a splitter in reverse. Channel 30 was unwatchable, 21 is great.
If the 2nd TV is cable-ready, change the TV2 output to something in the 70's. That will take it out of the OTA broadcast range. Maybe you are picking up some interference from OTA sources.