When the magnetic field of your picks comes close to the magnetic field of your amplifier’s output transformer, you have made a magnetic feedback loop. This tends to sound more like a squeal than musical feedback. This has nothing to do with the Power Station or attenuators in general.
Watch Joe demonstrate the mysterious squeal here:
A second type of mystery squeal is caused by having multiple paths to ground: “ground-loops”. Most users will have ground loops and will not even know about them, but this can be a problem when using high-gain amps and pedals.
This can be quite complicated to understand, but the solutions Joe demonstrates here are simple to implement:
