Nintendo DSi Quick Start Manual

Microphone Usage Precautions
Reduce the speaker volume if the microphone reacts
without any apparent input or produces feedback*.
When using software that utilises the built-in microphone,
sound coming from the speakers could cause the micro-
phone to respond randomly or cause feedback to occur.
* What is "Feedback"?
Feedback is the term used to refer to the high-pitched screeching
sound caused by a loop being created when sounds picked up by
the microphone are played back through the speakers and are then
picked up again by the microphone.
Microphone
if you experience feedback
Reduce the level of sound emanating from the speakers by either adjusting the
volume settings or attaching a pair of headphones.
Reduce the volume level
INTENDO.
PRINTED IN CHINA.