That stands for Sporadic Periodic Repetitive Annoying Interference Noise. Which I seem to get whenever I settle down to do a bit of recording.
http://up.metropol247.co.uk/Alexia/interference.mp3
Ignore the background hiss, I can weed that out - it's the two metallic-sounding bursts in the middle of the recording that I keep getting. It gets amplified and distorts the recording when actual words / music are put through the microphone.
Using a Soundblaster X-FI GO USB soundcard (although I have my inbuilt Realtek and a Maplins 5:1 USB soundcard adaptor availble too, the X-FI go is the only one that allows me to hear myself while recording)