Sounds like the sample rate doesnt match the sequence sample rate. Your sequence sample rate is most likely 48k….CD’s are natively at 44.1k.
The blue line area is rendered…and is probably playing fine.
The green line are is un-rendered and FCP is trying to sample rate convert on the fly…and not doing a good job of it.
Instead of rendering inside FCP or relying on FCP to sample rate convert on the fly, its better to convert the songs to 48k Stereo Uncompressed AIFF files using Compressor, iTunes or Quicktime Player before bringing them into FCP.