So I'm still having this issue and it's driving me nuts.. It happens with all channels, not just KDKA.. Here is a video of what I mean:
http://www.youtube.com/watch?v=cSMgUGbEXAk&hd=1
I have replaced one of the coax lines that runs from the antenna into the house but I still have it connecting to a coupler and then another 25' that goes to the TV that I didn't replace (thought 50' would be long enough)..
I didn't have any of these issues with my old antenna using the same cables (before replacing the 50' coax).
Any ideas?