If you turn up the Chat volume too high or if you turn on the Expander feature on the PX21 you may hear a subtle hiss during silent times. To minimize hiss while using the Expander or with the Chat volume cranked up, turn up the Chat level on the PS3 to maximum volume and lower the Chat volume on the PX21 so it isn't near its maximum setting. If you don't need the Expander you can turn it off to lower the hiss level.
If the hiss is too loud, the best way to test that would be to connect only the USB plug to a PC, then use that part of the PX21 for something like Skype, to hear what the mic sounds like. If it works OK on the PC, then it should work OK on Xbox or PS3. If it makes hiss on a PC, then most likely the USB chat interface on the PX21 is defective.
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