The problem, which appeared on dual 1.8GHz machines, created a beeping or hissing noise on some machines when used in conjunction with professional external audio gear, according to reports on Macintosh enthusiast sites including Think Secret and Macworld UK. The issue has also been a frequent topic of discussion on Apple's support site.
An Apple representative told CNET News.com that a "small number" of customers have experienced the problem, which has been fixed in production. The company said any customers experiencing the issue should contact the company's customer support.
Some consumers reported that a new power supply helped either reduce or eliminate the noise problem.
The Power Mac line has had some noise issues in the past. Last February, Apple started a program that allowed owners of some mirrored-door PowerMac G4 machines to get a that were designed to quiet the machines.