The PC speaker is normally meant to reproduce a square wave via only 2 levels of output (the speaker is driven by only two voltage levels, typically 0 V and 5 V).
For example, if your payments for March and July 2010 were each one month late, the report may continue to show (for seven years from the date after each payment was due) that you were 30 days late twice in 2010, even though the tradeline for that account also shows your payments for the rest of 2010 were made on time.
Your payment history (where delinquent payments show up) contributes the most to your credit score. Late payments generally stay on your credit report for seven years. Make sure you: Make all your payments on time. For most people, the easiest way to do this is to put all your bills on automatic payment.