Edit: After half day, my wife’s Mac started having the same problem. I have then applied the solution that I found in the Apple
Apple Release iTunes 10.5.2 To Public And Also Update Match Service
Apple earlier today released iTunes 10.5.2 to the public as well as upgrading the Match service which is still only available in the US. The update fixes a major problem which caused some songs to distort when imported from CD.
You can pick the update up in your software updates and also via the iTunes website
What’s new in iTunes 10.5.2
iTunes 10.5.2 includes several improvements for iTunes Match and fixes an audio distortion problem when playing or importing certain CDs.