You've got a couple of things going on there. There's the post-fact audit stuff, like "what if I pay off a car loan..". No, the act of paying the car loan early probably won't trigger anything by itself, but should you ever trigger any kind of tax audit from other behaviour (like, paying in $10,000 a week in cash bills), then that's exactly the sort of thing the auditors look for. ("Ah Mr Smith, nice Lamborghini. How did you pay for that ?" "oh, it was one of those ebay auctions that closes at a strange time and no-one else bid").

The second thing is the cash handling. On top of the regulatory limits (usually a $10,000 cash movement) which automatically trigger a report from the bank, there is also now much more "know your client" legislation in place following Sep 11 (eg Patriot Act). This requires an institution to file a report should you do anything which might seem a little odd, irrespective of any regulatory limits. Rolling up one sunny morning with a bag full of freshly printed bills might qualify as "a little odd".

Regards

Mark