Philco 38-4 questions

[darklife]

Just checked the speaker, now I know that is not the issue!
There is definitely feedback getting into the amplifier section from the RF section.
With volume all the way down, and even the dial disengaged (audio muted) I notice when turning the dial that I can hear RF feedback getting into the audio that sounds like hissing/squeeling. Changing the tone control effects this also. The problem seems to come and go at will.
Not sure how RF is getting back into the 6K5 tube but it must be. Tube shields are on by the way.
All capacitors check out fine so maybe it is just odd wire placement or something similar?
Stranger yet this only happens when the set is fed full line voltage. When I lower the voltage through a variac down to 100-110v the problem seems to goes away.

Edit: I tried a different 6A8G osc/det. tube that I had laying around and it seems to have cleared up the problem mentioned above. Not sure exactly why that is though.
Going to give it a few days of play and if no new problems pop up I am going to call it a done job since all seems to be working well and is playing nicely.
Thanks again everyone.