Dynaco Pas Makes ONE Pop Sound When Either Treble Control Is Turned From Center

When I turn either treble control from the center by-pass position there is a single slight pop out of the speaker. It only happens ONCE each time after the unit is turned on. You can then turn the treble controls from the center by-pass mode after the initial pop without any more pops. As stated, ONLY does this with the treble controls and only once after each new unit turn on. It's like a capacitor is being charged at turn on and then discharged after the control is turned. All the caps are new. Any clue what could be causing this?

Mine does that too. The treble control on the 3X has a special pot that is actually open circuited at the center. There are two capacitors connected to the ends of this pot, .02 and .002, but unfortunately when the treble pot is in the center these caps are completely out of the circuit and floating. My guess is they discharge internally over time and then when you move the pot away from center, one or the other is suddenly connected causing a surge flow which is heard as a pop.Only way I can think of to fix this would be to use a standard pot instead of the special one, but then you would lose the ability to have the treble control "out of the circuit". Or, just let it pop once and you'll probably be good for hours of playing.