Why are my burned opera CDRs distorting so badly?

I just burned several opera samplers on CDR.
Listening to these CDRs, there is a rather disturbing distortion that accompanies some of the vocal peaks; specifically, it is a rattling / cracking / breaking up distortion that seems to resonate sympathetically with extreme vocal volume peaks (it seems to be part of the soundfield, not localizing to either speaker).

It sounds like the recording microphones / recording equipment / master tape breaking up upon being overloaded.

However, if this is true, why isn't it apparent on any of the original CDs.
Found out it was the "Normalize" filter I was using on all of my audio compilations.