On both the Spike and JJP platforms, you may experience a "pop" noise when you power-down your machine.
The root cause of this noise is as follows. The power board and amplifier maintain their design voltage for a moment after the machine supply drops, so any shut-down noise present at the line out jack can result in a power down pop.
This varies from machine to machine, some having little at all. Its normal and won't cause a problem with your PinWoofer system.