Thank you all for the advice.
The rip speed with error correction is usually only 5 or 6X, although the drive is capable of more speed. I could try a new external drive.
Brand new CDs are having problems, but not always, and I am pretty sure the problem is in the error correction for flaws on the CD, since the transfer of other non-audio materials via CD seems flawless.
I will try MAX, perhaps it is better than XLD and iTunes.
I have considered adding a linear power supply to reduce noise and other power related issues that may be related to a switching power supply.
Once the music is on the hard drive properly, playback is flawless. Because the problem always occur on the same tracks, I do not think it is an output problem through the 2.0.
I have two more iMACs and a MacPower book. I will test the same CD on each of them with itunes and XLD and see what gives.
If I continue to have problems, I will take it to the Apple store and have them compare the CD ripping on two machines as suggested. I can see there is hope, but I may be re-ripping many CDs.