DC-DC boost converter voltage spike at power on, popping sound
The voltage spike you're seeing is because you're switching the power on. When you go from 0 volts to 3.3v in a couple of ms, that will appear as AC when your scope is set to AC. The issue is not your power supply, the issue is your audio driver that doesn't compensate for startup pops.

Edit:

One way might be to follow this suggestion like so







simulate this circuit &ndash; Schematic created using CircuitLab

R2 charges C2 up slowly, gradually turning on the mosfet over a couple of milliseconds, reducing the volume of the pop. You'll need to select an op amp that can handle the amount of power that you're putting into your speaker.