Every single resistor in my amp except for the fusibles and the metal oxide
on the nobel network are all 1% metal films. The amp is built with a 100%
ground plane on the circuit side. The ground is a single point where all
the grounds and signal returns terminate.
The bias adjust is 10 turn.
Yep, that's why you use metal film ones and I did, nearly throughout.
There's no need to use them throughout, only in a few critical positions - but personally (as I imagine with many others) I tend to use them everywhere, because I only stock metal film resistors.
Try again.
Nothing to try, normal amps don't do what you claim your's does - so it's design or construction errors in your amp.