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.
1 Closed accounts with no negative payment history: remain 10 years from the date they are closed. Positive accounts remain on your credit report longer than negative accounts.  Late payments remain seven years from the original delinquency date. A single late payment is deleted at seven years. If there was a series of late payments (not paid at 30 days, or 60 days, or 90 days) and then brought current, the payments would be deleted seven years from the first one missed in the series.