Internal microphone on iMacs: problem when used for video conferencing

Robert Blumenkranz (of ClearPhone) writes: "The internal microphone on almost all iMac (I have now conferenced with at least 100) are contaminated with a high pitched whining noise generated by the internal fans, disk drives, CD etc. To use the internal iMac microphone for video conferencing requires lowering the mic gain and you must talk loudly and directly into the microphone to be heard above this constant irritating noise. If you use an external PlainTalk microphone, it eliminates the noise completely." (Robert hopes that Apple will address and fix this problem.)