Have you tried another TV? Not the easiest diagnostic, I know, but circuitry can decay, often via failing capacitors.Very creative. And I am not above "hillbilly" tactics.
But I'm more interested in what is affecting the previously acceptable signals. Some have degraded over time and others are degraded for shorter periods at what seems like random times. We have twice replaced the antenna, even trying one with an amplifier. Sometimes it doesn't matter where you stand holding it.
Something is interfering. I'd love to know what but have no idea how to figure it out.
Another source of trouble can be trees growing up into your line-of-sight, causing variable signal absorption affected by rain and wind. Or new buildings. I once upon a time used a 5 cent 1/4 wave antenna made of a stick and zipcord, but new construction between us and the transmitter farm (6 stations in a 2 degree arc) drove me to a quad bow tie on a real mount.