Could you use a kymograph? You draw a line over the max intensity image of your stack and then use image->stack->reslice in ImageJ (or multikymograph included in Fiji)

Then the fluctuations of the tip position should appear rather clearly in the kymograph. Getting the tip position can then be done by overlapping a segmented line in the kymograph.

Cory and Pierre, thank you so much!! I will try both option!!