Penthode has good ideas.
GE was famous for crimping on RCA jacks & tons of
them went bad especially the UHF IF link. Light tapping,
moving things etc should smoke it out. It does sure
look IF related. Cold joints, loose screw, dirty tube socket or pins,
bad tube & poor grounds on shields. PCB to chassis grounds also.
BTW IF cable probably soldered on the tuner. If you are not careful
you can tear the jack out of the tuner. Heat it & gently rock & twist.
When it moves turn & lift at same time. The center pin is the perp.
73 Zeno
LFOD !