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.
Creditors usually report late payments to credit bureaus when you run 30 days or more past due. Late payments seriously damage your credit score and make it difficult to get credit, as well as saddle you with high interest rates. Late payments can stay on your credit report for years unless you can get them removed.