Yeah I`ve done it once in a 733 too. Makes a lot of noise but not a problem as long as you don`t retract it again until decreasing speed.
It will occur, when doing the after take-off checklist, if the microswitch is set too close to the neutral position and makes contact if the lever goes only a mm past. That was my excuse anyway and that particular aircraft did actually have an history of the gear re-appearing.
Like someone else said, you only do it once!