First, Dish DVRs use UHF for the 2nd TV... This can be a problem, I really wish I could flip VHF and UHF.. but alas, can not.
Now.... Things that can affect the picture
Low quality coax has more loss at higher frequencies but this would more likely cause SNOW than Waver.
MSW inverters can cause waver
Nearby FAN can cause waver (or any electrical motor) Does not matter if A/C or D/C.. Have cleared up more than a few headaches by suggesting a store clerk move her fan away from the monitor.
Beyond that I can not help much.
