it is probably analog. can you test with other TV? How about the other analog channels? It could be the tuner because it is funny that it clears as soon as you change to the channel. The analos signal is probably as powerfull as it was before so it could be a problem with your tuner. If it was the antenna system that it will not clear for second after you tune in. Very nice weather theses days so I see no other reason. But we need more info probably.