I have a Tv given to me from my parents when they got a big screen. It
is an RCA I think. It is a "CabinentTV" for lack of a better term.

It is my main TV in the living room. Even since my parents had it, when
watching "over air" channels, especially 2 and 4 all of a sudden the
picture goes out or gets week and there is a terible "shrieking". I can
jiggle the coax in the back and make it go away but it does it again. A
year or two ago I took the back off and my guess is it is something in
the coax connection on the tv itself. How would I go about diagnosing
and repairing this?