IMHO - it would have to be a heck of an overpayment in order to be money laundering - OR, there would have to be a LOT of loans with similar ties that have overpayments. Otherwise, if someone overpays a loan by, lets say, $200 - that is not a very efficient way of laundering money. Now if they overpaid it by $20,000, then you have something to look into.
I accidently overpaid a revolving card balance (I had automatic bill pay set up on my end and didn't stop it in time after the balance was reduced to zero), so there could be a number of reasons why an account overpaid.
Regulations are a poor substitute for ethics.