If it can be accessed by you in one or two quick moves, most courts would rule that you are carrying a dangerous weapon in a motor vehicle. May not be a problem if your vehicle is never searched but if you are pulled over, that machete may slide out from under the seat as you are applying the brakes. It would then be in "plain view", so what would have been a civil traffic citation will probably turn into a felony arrest on a weapons charge. Carry your machete in the trunk, locked up and out of sight. Why go looking for trouble?