Last PowerBook G4 models: sound problem?

I have bought a new PB in November 2005. As a professional musician, this computer can simply NOT be used (as for live or studio sessions). It seems that there are many reports about this problem.
Description: the sound enters into a loop for a couple of seconds, while the output level gets higher and higher still it saturates; then the audio output returns to normal. It happens randomly, but many times per day, and usually last for 6 to 7 seconds.
For a computer intended to be used by professional especially when a large number of musicians, artists, multimedia creators, or movie makers are using Mac for years; and also in relation to its price; one would expect not to get such a bug.
AppleSupport does not have any idea, even though the problem is known and the number of reports gets everyday higher; as shown in this subject:
http://discussions.apple.com/thread.jspa?messageID=1589957
Apple does not propose any fix, but also does not communicate, neither acknowledge the problem. There is only one document referring to this issue ( http://docs.info.apple.com/article.html?artnum=302978), and it recommends to avoid running several audio applications simultaneously... no comment...
blockquote>Of course, the number of users facing this problem is relatively small but it is composed of longtime Mac users and in most cases professionals.
A website has been created to collect reports and bring the issue to Apple's ears: http://PowerBookDefect.info/
Let's expect that Apple will hear them complaining about this problem, which prevent them to work properly with their computers.