Squeal in the 77 Pentode channel

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My build called Phirty6 has a unusual tube combination intended to replicate the tubes from the Philco car radio it was built from.
Triode and pentode channels each feeding a SE pentode.
More here https://stillampd.com/phirty6
It has been "working well" for some time.
Today I added a switch jack to allow an external speaker to be connected.

But as I played it, I discovered that the pentode channel (and the combined channel) had a squeal (maybe always there?). Other squeal resulted with the strat when played through the bridge pup. And squeal when the guitar is removed but the cable left in amp.
Maybe a RF pickup issue? Maybe microphonic 77 tube?
Any other thoughts?

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Tube was not the problem tried a couple of 77s in the pre-pentode position.
But adding a small .01 cap across the 1M resistor at the input jack and the squeal is gone.
inspiration from https://el34world.com/Forum/index.php?topic=9482.msg362552#msg362552

Still have too much amp noise at high volume that needs investigation.
No input and increases with volume

[shooter]

too much amp noise at high volume that needs investigation.

switch n relay contacts can be A sneaky path for noise even when they ohm "shorted"

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The noise was because the speaker magnet was sitting really close to the pentode preamp tube.
I'm a pack rat and keep everything; luckily found the original shield for that tube (was a 78 remote cutoff in radio now a 77 sharp cutoff in guitar amp same size tube as they are evil twins) and with a bit of modification got the shield and the speaker to fit. Noise much less.

I gutted everything from the radio no relays or switches remain for noise paths.
Unless you refer to something else.

[Willabe]

The noise was because the speaker magnet was sitting really close to the pentode preamp tube.

My 1st build was a 5E3 clone, came out fine, no problems at 1st turn on.

Then I put it in a 5E3/single 12" speaker cab clone I built. 1 of the 6V6's lit up like a light bulb.       

I had centered the speaker in the baffle and that put the speaker magnet to close to the 6V6. Made a new baffle, moved the speaker cut out down and to the right, looking from the back, and that fixed it.

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I also added a tube shield to the triode Preamp although triode channel wasn't too noisy.
The second stage 75 tube would not fit a shield with the 6" Eminence guitar speaker I have in this.
Magnet of the Eminence is much larger than the original.
Also used this time as an opportunity to make a speaker attachment "collar" because the "baffle" screw holes do not match the modern speaker holes. Always improving.