I have an iMac G5, a Matshita burner, the latest version of iTunes, and I am using Memorex CD-Rs. I've read some forums about this problem with MacBooks, but their advice to slow down the write speed to 16X hasn't helped. I have burned many CDs using this same medium, and with this latest version of iTunes without a problem, but now I can only burn a few songs before a loud noise, rather like grinding, starts and eventually the error message: "Attempt to burn a disc failed. Burn failed due to a medium write error." pops up. Is it a software or a hardware problem? I would appreciate any help, as I have a lot of discs to burn, and soon.