Hard to guess what might be wrong, but one possibility is that the new audio files are in MP3 or other compressed format that is not well handled by Premiere. Worth checking that your ripper is generating WAV files with suitable parameters for use in Premiere.
Another possibility is (if you are using a non-Pro Premiere) that Premiere has defaulted to less than full quality on audio rate conversions (CD rips tend to be at 44.1, whilst DV is at 32 or 48k). If this might apply to you, check in the audio settings and set best rate conversion. This does not apply to Premiere Pro, which conforms all the audio before you can start editing.