Mistracking removes part of the waveform and causes distortion. One of the best seat-of-the-pants tests for me was to listen to "Dear Diary" from the Moody Blues. The vocals on that song seem to really chatter an underloaded cartridge. I can always hear it when the tone arm was too light for the needle on that song. So if I'm somewhere that I don't have a test record and a scope handy for a first-time setup, I could always count on that for a reasonably good indicator of needle chatter. Another good one is Yes - Fragile, where practically all of the tracks containing piano will show the problem if it's there.