Seems like maybe you have access to some "inside" information on the industry. If you do, it would help to know what country and/or states see the higher than normal car rental volume for October. That might give us some clues as to why.

In the US, October does have one holiday - Columbus day - which a fair number of people don't have to work, thus creating a nice 3-day weekend. Alamo has had this weekend blacked out nationwide for using miles/point awards for at least the last three years. In the northeast, and in many other parts of the US as well, October marks the last sustained period of nice weather before winter sets in. If your October data shows numerous short (i.e., 2 or 3 day weekend) rentals, this may support people feeling the urge to get away one last time before the cold. If the rentals/requests are for longer periods of time, something else is probably going on.

Is there anything you can share with us to help us narrow the possibilities?