How often should banks be checking their website for ADA compliance?

If a bank has a policy of checking their website quarterly and between quarterly reviews, you perform a review for an audit and find an issue, how do you approach it in your report?

Finally, based on the bank's size, there are several free online tools that can check for ADA compliance. However, the results from one tool to the next never seem to be consistent. One might list several critical issues while another may only list the issue as needing attention (but not critical). How do you reconcile the differences of classification?