Also ensure your booster is off on theroof antenna or that also happens. Usually the green light will be on if the 12volt booster is in the on position. If it is just push the little black button beside it and it should go out.
Had some similar problems on my just finished trip. Did what Dalemac and speedster suggested to no avail. Realized that I was using a really old coax from my house between the outlet and the TV, probably '80s vintage and replaced it. Problem solved.
Thanks for all the help. I found a couple connections that were a lil loose, tightened em up and that helped. I noticed my cable I use to hookup with has a couple small cracks in it. Gonna pick up a new one, that should help too.