Sounds like antenna problems. Check for corrosion or rubbing through of the cable somewhere.
Some years back a friend of mine was watching TV one night when the set started making frying noises a emitting smoke. On investigation, he found the inside of the set was soaking wet. It turned out that the cable had rubbed on the edge of the rainwater gutter and water had got into the core of the cable which acted as a pipe transferring it into the guts of the set!
