OK, so i think i've figured it out... all it took was for me to post my first question on this forum :p
It's definitely a reflection from the IR LED's, and it's a reflection from one of the rear red reflector lenses on my vehicle parked in the driveway.
I figured this out by turning off the IR LED's and then turning them back on again. When the IR LED's were off, the little white circle disappeared. When i turned it back on, the white circle reappeared (and i noticed a huge amount of reflection from the rear red reflector lense). So there you have it.
I've read about people getting reflections from the window when pointing indoor cameras outside at night, but never thought i'd experience such a reflection with the camera mounted outdoors... live and learn. On to the next little thing that's bugging me...