[P1] Turning off built-in mic on iBook?

[rusty57]

 able to turn it down, but not off. 
>> Even with the slider 
>> in the "off" position, I'm getting a little input. 
>> I can snap my 
>> fingers (or type loudly) and still see a reading on
>> the input level 
>> meter.

My daughter corrected a similar problem on her iMac DV400 by plugging in 
an external mic then unplugging it- for some reason her built-in mic was 
on at full volume and wouldn't respond to any changes to the control 
panel - now it works fine.