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.
Having just ONE late payment on your credit report can be devastating to you credit scores. Late payments can stay on your credit report for 7 years. However, contrary to popular belief, you do NOT have to wait up to 7 years before being able to get a mortgage, car loan or any other type of credit again.