[rghines1]

This may be the dreaded silver mica disease inside the IF transformers. The schematic shows they are adjusted with the ferrite slugs which are the most prone to this problem.

If so you are likely hearing some static thunderstorms. Sometimes use a simple RF grounding probe that is easy to build. Take a old test probe and wire a 0.1uf 630V poly cap in series with the probe. Connect one of the probe to -B with the other end used to ground out tube pins such as plate and grid. With patience it is possible to isolate the problem to a particular stage with the divide and conquer approach.

Richard